diff --git a/src/plugins/coreplugin/navigationsubwidget.cpp b/src/plugins/coreplugin/navigationsubwidget.cpp
index 00bbd969e00..39c23b45bd3 100644
--- a/src/plugins/coreplugin/navigationsubwidget.cpp
+++ b/src/plugins/coreplugin/navigationsubwidget.cpp
@@ -194,6 +194,11 @@ void NavigationSubWidget::setCloseIcon(const QIcon &icon)
     m_closeButton->setIcon(icon);
 }
 
+QWidget *NavigationSubWidget::widget()
+{
+    return m_navigationWidget;
+}
+
 int NavigationSubWidget::factoryIndex() const
 {
     return m_navigationComboBox->currentIndex();
diff --git a/src/plugins/coreplugin/navigationsubwidget.h b/src/plugins/coreplugin/navigationsubwidget.h
index 6d49c850269..c19e66b3ecc 100644
--- a/src/plugins/coreplugin/navigationsubwidget.h
+++ b/src/plugins/coreplugin/navigationsubwidget.h
@@ -72,6 +72,8 @@ public:
     Command *command(const QString &title) const;
     void setCloseIcon(const QIcon &icon);
 
+    QWidget *widget();
+
 signals:
     void splitMe(int factoryIndex);
     void closeMe();
diff --git a/src/plugins/coreplugin/navigationwidget.cpp b/src/plugins/coreplugin/navigationwidget.cpp
index d262591c568..079656fb0d3 100644
--- a/src/plugins/coreplugin/navigationwidget.cpp
+++ b/src/plugins/coreplugin/navigationwidget.cpp
@@ -270,14 +270,14 @@ void NavigationWidget::activateSubWidget()
     activateSubWidget(id);
 }
 
-void NavigationWidget::activateSubWidget(Id factoryId)
+QWidget *NavigationWidget::activateSubWidget(Id factoryId)
 {
     setShown(true);
     foreach (Internal::NavigationSubWidget *subWidget, d->m_subWidgets) {
         if (subWidget->factory()->id() == factoryId) {
             subWidget->setFocusWidget();
             ICore::raiseWindow(this);
-            return;
+            return subWidget->widget();
         }
     }
 
@@ -286,6 +286,7 @@ void NavigationWidget::activateSubWidget(Id factoryId)
         d->m_subWidgets.first()->setFactoryIndex(index);
         d->m_subWidgets.first()->setFocusWidget();
         ICore::raiseWindow(this);
+        return d->m_subWidgets.first()->widget();
     }
 }
 
diff --git a/src/plugins/coreplugin/navigationwidget.h b/src/plugins/coreplugin/navigationwidget.h
index f83356d6d9e..ea9ad776043 100644
--- a/src/plugins/coreplugin/navigationwidget.h
+++ b/src/plugins/coreplugin/navigationwidget.h
@@ -87,7 +87,7 @@ public:
     void saveSettings(QSettings *settings);
     void restoreSettings(QSettings *settings);
 
-    void activateSubWidget(Id factoryId);
+    QWidget *activateSubWidget(Id factoryId);
     void closeSubWidgets();
 
     bool isShown() const;
diff --git a/src/plugins/cpptools/cpptoolstestcase.cpp b/src/plugins/cpptools/cpptoolstestcase.cpp
index 8cd7953320e..b54d6c4ace5 100644
--- a/src/plugins/cpptools/cpptoolstestcase.cpp
+++ b/src/plugins/cpptools/cpptoolstestcase.cpp
@@ -286,13 +286,13 @@ ProjectOpenerAndCloser::~ProjectOpenerAndCloser()
 
 ProjectInfo ProjectOpenerAndCloser::open(const QString &projectFile, bool configureAsExampleProject)
 {
-    QString error;
-    Project *project = ProjectExplorerPlugin::openProject(projectFile, &error);
-    if (!error.isEmpty())
-        qWarning() << error;
-    if (!project)
+    ProjectExplorerPlugin::OpenProjectResult result = ProjectExplorerPlugin::openProject(projectFile);
+    if (!result) {
+        qWarning() << result.errorMessage() << result.alreadyOpen();
         return ProjectInfo();
+    }
 
+    Project *project = result.project();
     if (configureAsExampleProject)
         project->configureAsExampleProject(QStringList());
 
diff --git a/src/plugins/debugger/debuggerplugin.cpp b/src/plugins/debugger/debuggerplugin.cpp
index d072df0c3bd..11875becead 100644
--- a/src/plugins/debugger/debuggerplugin.cpp
+++ b/src/plugins/debugger/debuggerplugin.cpp
@@ -3245,15 +3245,15 @@ void DebuggerPluginPrivate::testLoadProject(const QString &proFile, const TestCa
             this, &DebuggerPluginPrivate::testProjectLoaded);
 
     m_testCallbacks.append(cb);
-    QString error;
-    if (ProjectExplorerPlugin::openProject(proFile, &error)) {
+    ProjectExplorerPlugin::OpenProjectResult result = ProjectExplorerPlugin::openProject(proFile);
+    if (result) {
         // Will end up in callback below due to the connections to
         // signal currentProjectChanged().
         return;
     }
 
     // Project opening failed. Eat the unused callback.
-    qWarning("Cannot open %s: %s", qPrintable(proFile), qPrintable(error));
+    qWarning("Cannot open %s: %s", qPrintable(proFile), qPrintable(result.errorMessage()));
     QVERIFY(false);
     m_testCallbacks.pop_back();
 }
diff --git a/src/plugins/projectexplorer/customwizard/customwizard.cpp b/src/plugins/projectexplorer/customwizard/customwizard.cpp
index 69d24364b82..00fb0d1c686 100644
--- a/src/plugins/projectexplorer/customwizard/customwizard.cpp
+++ b/src/plugins/projectexplorer/customwizard/customwizard.cpp
@@ -525,8 +525,12 @@ bool CustomProjectWizard::postGenerateOpen(const Core::GeneratedFiles &l, QStrin
     // Post-Generate: Open the project and the editors as desired
     foreach (const Core::GeneratedFile &file, l) {
         if (file.attributes() & Core::GeneratedFile::OpenProjectAttribute) {
-            if (!ProjectExplorerPlugin::openProject(file.path(), errorMessage))
+            ProjectExplorerPlugin::OpenProjectResult result
+                    = ProjectExplorerPlugin::openProject(file.path());
+            if (!result) {
                 return false;
+                *errorMessage = result.errorMessage();
+            }
         }
     }
     return BaseFileWizardFactory::postGenerateOpenEditors(l, errorMessage);
diff --git a/src/plugins/projectexplorer/jsonwizard/jsonwizard.cpp b/src/plugins/projectexplorer/jsonwizard/jsonwizard.cpp
index 035eae6d64a..982c4b6aee3 100644
--- a/src/plugins/projectexplorer/jsonwizard/jsonwizard.cpp
+++ b/src/plugins/projectexplorer/jsonwizard/jsonwizard.cpp
@@ -309,8 +309,10 @@ void JsonWizard::openFiles(const JsonWizard::GeneratorFiles &files)
             break;
         }
         if (file.attributes() & Core::GeneratedFile::OpenProjectAttribute) {
-            Project *project = ProjectExplorerPlugin::instance()->openProject(file.path(), &errorMessage);
-            if (!project) {
+            ProjectExplorerPlugin::OpenProjectResult result
+                    = ProjectExplorerPlugin::instance()->openProject(file.path());
+            if (!result) {
+                errorMessage = result.errorMessage();
                 if (errorMessage.isEmpty()) {
                     errorMessage = QCoreApplication::translate("ProjectExplorer::JsonWizard",
                                                                "Failed to open \"%1\" as a project.")
diff --git a/src/plugins/projectexplorer/projectexplorer.cpp b/src/plugins/projectexplorer/projectexplorer.cpp
index 4ee86039e4e..be62a91fbcc 100644
--- a/src/plugins/projectexplorer/projectexplorer.cpp
+++ b/src/plugins/projectexplorer/projectexplorer.cpp
@@ -1410,11 +1410,11 @@ void ProjectExplorerPluginPrivate::loadAction()
                                                     dd->m_projectFilterString);
     if (filename.isEmpty())
         return;
-    QString errorMessage;
-    ProjectExplorerPlugin::openProject(filename, &errorMessage);
 
-    if (!errorMessage.isEmpty())
-        QMessageBox::critical(ICore::mainWindow(), tr("Failed to open project."), errorMessage);
+    ProjectExplorerPlugin::OpenProjectResult result = ProjectExplorerPlugin::openProject(filename);
+    if (!result)
+        ProjectExplorerPlugin::showOpenProjectError(result);
+
     updateActions();
 }
 
@@ -1495,11 +1495,10 @@ void ProjectExplorerPlugin::extensionsInitialized()
 
     auto factory = new IDocumentFactory;
     factory->setOpener([this](const QString &fileName) -> IDocument* {
-        QString errorMessage;
-        ProjectExplorerPlugin::openProject(fileName, &errorMessage);
-        if (!errorMessage.isEmpty())
-            QMessageBox::critical(ICore::mainWindow(),
-                tr("Failed to open project."), errorMessage);
+
+        OpenProjectResult result = ProjectExplorerPlugin::openProject(fileName);
+        if (!result)
+            showOpenProjectError(result);
         return 0;
     });
 
@@ -1653,23 +1652,52 @@ void ProjectExplorerPluginPrivate::savePersistentSettings()
 
 void ProjectExplorerPlugin::openProjectWelcomePage(const QString &fileName)
 {
-    QString errorMessage;
-    openProject(fileName, &errorMessage);
-    if (!errorMessage.isEmpty())
-        QMessageBox::critical(ICore::mainWindow(), tr("Failed to Open Project"), errorMessage);
+    OpenProjectResult result = openProject(fileName);
+    if (!result)
+        showOpenProjectError(result);
 }
 
-Project *ProjectExplorerPlugin::openProject(const QString &fileName, QString *errorString)
+ProjectExplorerPlugin::OpenProjectResult ProjectExplorerPlugin::openProject(const QString &fileName)
 {
     if (debug)
         qDebug() << "ProjectExplorerPlugin::openProject";
 
-    QList<Project *> list = openProjects(QStringList() << fileName, errorString);
-    if (list.isEmpty())
-        return 0;
-    dd->addToRecentProjects(fileName, list.first()->displayName());
-    SessionManager::setStartupProject(list.first());
-    return list.first();
+    OpenProjectResult result = openProjects(QStringList() << fileName);
+    Project *project = result.project();
+    if (!project)
+        return result;
+    dd->addToRecentProjects(fileName, project->displayName());
+    SessionManager::setStartupProject(project);
+    return result;
+}
+
+void ProjectExplorerPlugin::showOpenProjectError(const OpenProjectResult &result)
+{
+    if (result)
+        return;
+
+    // Potentially both errorMessage and alreadyOpen could contain information
+    // that should be shown to the user.
+    // BUT, if Creator opens only a single project, this can lead
+    // to either
+    // - No error
+    // - A errorMessage
+    // - A single project in alreadyOpen
+
+    // The only place where multiple projects are opened is in session restore
+    // where the already open case should never happen, thus
+    // the following code uses those assumptions to make the code simpler
+
+    QString errorMessage = result.errorMessage();
+    if (!errorMessage.isEmpty()) {
+        // ignore alreadyOpen
+        QMessageBox::critical(ICore::mainWindow(), tr("Failed to Open Project"), errorMessage);
+    } else {
+        // ignore multiple alreadyOpen
+        Project *alreadyOpen = result.alreadyOpen().first();
+        ProjectTree::highlightProject(alreadyOpen,
+                                      tr("<h3>Project already open</h3>"));
+    }
 }
 
 static QList<IProjectManager*> allProjectManagers()
@@ -1677,17 +1705,17 @@ static QList<IProjectManager*> allProjectManagers()
     return ExtensionSystem::PluginManager::getObjects<IProjectManager>();
 }
 
-static void appendError(QString *errorString, const QString &error)
+static void appendError(QString &errorString, const QString &error)
 {
-    if (!errorString || error.isEmpty())
+    if (error.isEmpty())
         return;
 
-    if (!errorString->isEmpty())
-        errorString->append(QLatin1Char('\n'));
-    errorString->append(error);
+    if (!errorString.isEmpty())
+        errorString.append(QLatin1Char('\n'));
+    errorString.append(error);
 }
 
-QList<Project *> ProjectExplorerPlugin::openProjects(const QStringList &fileNames, QString *errorString)
+ProjectExplorerPlugin::OpenProjectResult ProjectExplorerPlugin::openProjects(const QStringList &fileNames)
 {
     if (debug)
         qDebug() << "ProjectExplorerPlugin - opening projects " << fileNames;
@@ -1695,6 +1723,8 @@ QList<Project *> ProjectExplorerPlugin::openProjects(const QStringList &fileName
     const QList<IProjectManager*> projectManagers = allProjectManagers();
 
     QList<Project*> openedPro;
+    QList<Project *> alreadyOpen;
+    QString errorString;
     foreach (const QString &fileName, fileNames) {
         QTC_ASSERT(!fileName.isEmpty(), continue);
 
@@ -1705,13 +1735,12 @@ QList<Project *> ProjectExplorerPlugin::openProjects(const QStringList &fileName
         bool found = false;
         foreach (Project *pi, SessionManager::projects()) {
             if (filePath == pi->projectFilePath().toString()) {
+                alreadyOpen.append(pi);
                 found = true;
                 break;
             }
         }
         if (found) {
-            appendError(errorString, tr("Failed opening project \"%1\": Project already open.")
-                        .arg(QDir::toNativeSeparators(fileName)));
             SessionManager::reportProjectLoadingProgress();
             continue;
         }
@@ -1767,7 +1796,7 @@ QList<Project *> ProjectExplorerPlugin::openProjects(const QStringList &fileName
         ModeManager::setFocusToCurrentMode();
     }
 
-    return openedPro;
+    return OpenProjectResult(openedPro, alreadyOpen, errorString);
 }
 
 void ProjectExplorerPluginPrivate::updateWelcomePage()
@@ -2900,10 +2929,10 @@ void ProjectExplorerPluginPrivate::openRecentProject(const QString &fileName)
         qDebug() << "ProjectExplorerPlugin::openRecentProject()";
 
     if (!fileName.isEmpty()) {
-        QString errorMessage;
-        ProjectExplorerPlugin::openProject(fileName, &errorMessage);
-        if (!errorMessage.isEmpty())
-            QMessageBox::critical(ICore::mainWindow(), tr("Failed to open project."), errorMessage);
+        ProjectExplorerPlugin::OpenProjectResult result
+                = ProjectExplorerPlugin::openProject(fileName);
+        if (!result)
+            ProjectExplorerPlugin::showOpenProjectError(result);
     }
 }
 
diff --git a/src/plugins/projectexplorer/projectexplorer.h b/src/plugins/projectexplorer/projectexplorer.h
index 61d86e65aaa..9491b73bd65 100644
--- a/src/plugins/projectexplorer/projectexplorer.h
+++ b/src/plugins/projectexplorer/projectexplorer.h
@@ -72,8 +72,48 @@ public:
 
     static ProjectExplorerPlugin *instance();
 
-    static Project *openProject(const QString &fileName, QString *error);
-    static QList<Project *> openProjects(const QStringList &fileNames, QString *error);
+    class OpenProjectResult
+    {
+    public:
+        OpenProjectResult(QList<Project *> projects, QList<Project *> alreadyOpen,
+                          const QString &errorMessage)
+            : m_projects(projects), m_alreadyOpen(alreadyOpen),
+              m_errorMessage(errorMessage)
+        {}
+
+        explicit operator bool() const
+        {
+            return m_errorMessage.isEmpty() && m_alreadyOpen.isEmpty();
+        }
+
+        Project *project() const
+        {
+            return m_projects.isEmpty() ? 0 : m_projects.first();
+        }
+
+        QList<Project *> projects() const
+        {
+            return m_projects;
+        }
+
+        QString errorMessage() const
+        {
+            return m_errorMessage;
+        }
+
+        QList<Project *> alreadyOpen() const
+        {
+            return m_alreadyOpen;
+        }
+    private:
+        QList<Project *> m_projects;
+        QList<Project *> m_alreadyOpen;
+        QString m_errorMessage;
+    };
+
+    static OpenProjectResult openProject(const QString &fileName);
+    static OpenProjectResult openProjects(const QStringList &fileNames);
+    static void showOpenProjectError(const OpenProjectResult &result);
     Q_SLOT void openProjectWelcomePage(const QString &fileName);
     static void unloadProject(Project *project);
 
diff --git a/src/plugins/projectexplorer/projectexplorerconstants.h b/src/plugins/projectexplorer/projectexplorerconstants.h
index 0efa68577f8..d96c3759b34 100644
--- a/src/plugins/projectexplorer/projectexplorerconstants.h
+++ b/src/plugins/projectexplorer/projectexplorerconstants.h
@@ -277,6 +277,9 @@ const char QML_PROFILER_RUN_MODE[]="RunConfiguration.QmlProfilerRunMode";
 const char DEBUG_RUN_MODE[]="RunConfiguration.DebugRunMode";
 const char DEBUG_RUN_MODE_WITH_BREAK_ON_MAIN[]="RunConfiguration.DebugRunModeWithBreakOnMain";
 
+// Navigation Widget
+const char PROJECTTREE_ID[] = "Projects";
+
 } // namespace Constants
 } // namespace ProjectExplorer
 
diff --git a/src/plugins/projectexplorer/projecttree.cpp b/src/plugins/projectexplorer/projecttree.cpp
index 691b616b0eb..ddc858835ea 100644
--- a/src/plugins/projectexplorer/projecttree.cpp
+++ b/src/plugins/projectexplorer/projecttree.cpp
@@ -46,6 +46,8 @@
 #include <coreplugin/actionmanager/actioncontainer.h>
 #include <coreplugin/actionmanager/actionmanager.h>
 #include <coreplugin/documentmanager.h>
+#include <coreplugin/navigationwidget.h>
+#include <coreplugin/modemanager.h>
 
 #include <QApplication>
 #include <QMenu>
@@ -531,6 +533,19 @@ void ProjectTree::showContextMenu(ProjectTreeWidget *focus, const QPoint &global
     }
 }
 
+void ProjectTree::highlightProject(Project *project, const QString &message)
+{
+
+    Core::ModeManager::activateMode(Core::Constants::MODE_EDIT);
+    Core::NavigationWidget *navigation = Core::NavigationWidget::instance();
+
+    // Shows and focusses a project tree
+    QWidget *widget = navigation->activateSubWidget(ProjectExplorer::Constants::PROJECTTREE_ID);
+
+    if (auto *projectTreeWidget = qobject_cast<ProjectTreeWidget *>(widget))
+        projectTreeWidget->showMessage(project->rootProjectNode(), message);
+}
+
 void ProjectTree::hideContextMenu()
 {
     m_focusForContextMenu = 0;
diff --git a/src/plugins/projectexplorer/projecttree.h b/src/plugins/projectexplorer/projecttree.h
index 5f74f157188..7e26f436305 100644
--- a/src/plugins/projectexplorer/projecttree.h
+++ b/src/plugins/projectexplorer/projecttree.h
@@ -66,6 +66,8 @@ public:
 
     static void showContextMenu(Internal::ProjectTreeWidget *focus, const QPoint &globalPos, Node *node);
 
+    static void highlightProject(Project *project, const QString &message);
+
 signals:
     void currentProjectChanged(ProjectExplorer::Project *project);
     void currentNodeChanged(ProjectExplorer::Node *node, ProjectExplorer::Project *project);
diff --git a/src/plugins/projectexplorer/projecttreewidget.cpp b/src/plugins/projectexplorer/projecttreewidget.cpp
index 29a51c1a734..5b37b09432e 100644
--- a/src/plugins/projectexplorer/projecttreewidget.cpp
+++ b/src/plugins/projectexplorer/projecttreewidget.cpp
@@ -48,6 +48,7 @@
 
 #include <utils/navigationtreeview.h>
 #include <utils/algorithm.h>
+#include <utils/tooltip/tooltip.h>
 
 #include <QDebug>
 #include <QSettings>
@@ -480,6 +481,17 @@ void ProjectTreeWidget::sync(Node *node)
         setCurrentItem(node);
 }
 
+void ProjectTreeWidget::showMessage(Node *node, const QString &message)
+{
+    QModelIndex idx = m_model->indexForNode(node);
+    m_view->setCurrentIndex(idx);
+    m_view->scrollTo(idx);
+
+    QPoint pos = m_view->mapToGlobal(m_view->visualRect(idx).bottomLeft());
+    pos -= Utils::ToolTip::offsetFromPosition();
+    Utils::ToolTip::show(pos, message);
+}
+
 void ProjectTreeWidget::showContextMenu(const QPoint &pos)
 {
     QModelIndex index = m_view->indexAt(pos);
@@ -563,7 +575,7 @@ ProjectTreeWidgetFactory::ProjectTreeWidgetFactory()
 {
     setDisplayName(tr("Projects"));
     setPriority(100);
-    setId("Projects");
+    setId(ProjectExplorer::Constants::PROJECTTREE_ID);
     setActivationSequence(QKeySequence(UseMacShortcuts ? tr("Meta+X") : tr("Alt+X")));
 }
 
diff --git a/src/plugins/projectexplorer/projecttreewidget.h b/src/plugins/projectexplorer/projecttreewidget.h
index 3ebca208e84..8e093cd8d04 100644
--- a/src/plugins/projectexplorer/projecttreewidget.h
+++ b/src/plugins/projectexplorer/projecttreewidget.h
@@ -68,6 +68,7 @@ public:
     QToolButton *toggleSync();
     Node *currentNode();
     void sync(ProjectExplorer::Node *node);
+    void showMessage(ProjectExplorer::Node *node, const QString &message);
 
     static Node *nodeForFile(const Utils::FileName &fileName);
     static Node *mostExpandedNode(const QList<Node*> &nodes);
diff --git a/src/plugins/projectexplorer/session.cpp b/src/plugins/projectexplorer/session.cpp
index 3d70dc9addc..820e0287df7 100644
--- a/src/plugins/projectexplorer/session.cpp
+++ b/src/plugins/projectexplorer/session.cpp
@@ -870,11 +870,10 @@ void SessionManagerPrivate::restoreProjects(const QStringList &fileList)
     // Keep projects that failed to load in the session!
     m_failedProjects = fileList;
     if (!fileList.isEmpty()) {
-        QString errors;
-        QList<Project *> projects = ProjectExplorerPlugin::openProjects(fileList, &errors);
-        if (!errors.isEmpty())
-            QMessageBox::critical(ICore::mainWindow(), SessionManager::tr("Failed to open project"), errors);
-        foreach (Project *p, projects)
+        ProjectExplorerPlugin::OpenProjectResult result = ProjectExplorerPlugin::openProjects(fileList);
+        if (!result)
+            ProjectExplorerPlugin::showOpenProjectError(result);
+        foreach (Project *p, result.projects())
             m_failedProjects.removeAll(p->projectFilePath().toString());
     }
 }
diff --git a/src/plugins/qtsupport/gettingstartedwelcomepage.cpp b/src/plugins/qtsupport/gettingstartedwelcomepage.cpp
index 4268c645ccc..eedda4cea5b 100644
--- a/src/plugins/qtsupport/gettingstartedwelcomepage.cpp
+++ b/src/plugins/qtsupport/gettingstartedwelcomepage.cpp
@@ -412,18 +412,19 @@ void ExamplesWelcomePage::openProject(const QString &projectFile,
     }
 
     // don't try to load help and files if loading the help request is being cancelled
-    QString errorMessage;
     if (proFile.isEmpty())
         return;
-    if (ProjectExplorer::ProjectExplorerPlugin::instance()->openProject(proFile, &errorMessage)) {
+    ProjectExplorer::ProjectExplorerPlugin::OpenProjectResult result =
+            ProjectExplorer::ProjectExplorerPlugin::instance()->openProject(proFile);
+    if (result) {
         Core::ICore::openFiles(filesToOpen);
         Core::ModeManager::activateMode(Core::Constants::MODE_EDIT);
         if (help.isValid())
             openHelpInExtraWindow(help.toString());
         Core::ModeManager::activateMode(ProjectExplorer::Constants::MODE_SESSION);
+    } else {
+        ProjectExplorer::ProjectExplorerPlugin::showOpenProjectError(result);
     }
-    if (!errorMessage.isEmpty())
-        QMessageBox::critical(Core::ICore::mainWindow(), tr("Failed to Open Project"), errorMessage);
 }
 
 ExamplesListModel *ExamplesWelcomePage::examplesModel() const