diff --git a/app/src/cc/arduino/contributions/libraries/ui/LibraryManagerUI.java b/app/src/cc/arduino/contributions/libraries/ui/LibraryManagerUI.java
index 3aac99ba0..bca4e05d2 100644
--- a/app/src/cc/arduino/contributions/libraries/ui/LibraryManagerUI.java
+++ b/app/src/cc/arduino/contributions/libraries/ui/LibraryManagerUI.java
@@ -79,7 +79,7 @@ public class LibraryManagerUI extends InstallerJDialog {
   }
 
   public LibraryManagerUI(Frame parent) {
-    super(parent, "Library Manager", Dialog.ModalityType.APPLICATION_MODAL);
+    super(parent, "Library Manager", Dialog.ModalityType.APPLICATION_MODAL, _("No internet connection available, the list of available libraries is not complete. You will be able to manage only the libraries you've already installed."));
   }
 
   public void setIndexer(LibrariesIndexer indexer) {
@@ -155,7 +155,7 @@ public class LibraryManagerUI extends InstallerJDialog {
         }
       }
     });
-    installerThread.setUncaughtExceptionHandler(new InstallerJDialogUncaughtExceptionHandler(this));
+    installerThread.setUncaughtExceptionHandler(new InstallerJDialogUncaughtExceptionHandler(this, noConnectionErrorMessage));
     installerThread.start();
   }
 
@@ -176,7 +176,7 @@ public class LibraryManagerUI extends InstallerJDialog {
         }
       }
     });
-    installerThread.setUncaughtExceptionHandler(new InstallerJDialogUncaughtExceptionHandler(this));
+    installerThread.setUncaughtExceptionHandler(new InstallerJDialogUncaughtExceptionHandler(this, noConnectionErrorMessage));
     installerThread.start();
   }
 
@@ -184,7 +184,7 @@ public class LibraryManagerUI extends InstallerJDialog {
     boolean managedByIndex = indexer.getIndex().getLibraries().contains(lib);
 
     if (!managedByIndex) {
-      int chosenOption = JOptionPane.showConfirmDialog(getParent(), _("This library is not listed on Library Manager. You won't be able to resinstall it from here.\nAre you sure you want to delete it?"), _("Please confirm library deletion"), JOptionPane.YES_NO_OPTION, JOptionPane.QUESTION_MESSAGE);
+      int chosenOption = JOptionPane.showConfirmDialog(getParent(), _("This library is not listed on Library Manager. You won't be able to resinstall it from here.<br/>Are you sure you want to delete it?"), _("Please confirm library deletion"), JOptionPane.YES_NO_OPTION, JOptionPane.QUESTION_MESSAGE);
       if (chosenOption != JOptionPane.YES_OPTION) {
         return;
       }
@@ -206,7 +206,7 @@ public class LibraryManagerUI extends InstallerJDialog {
         }
       }
     });
-    installerThread.setUncaughtExceptionHandler(new InstallerJDialogUncaughtExceptionHandler(this));
+    installerThread.setUncaughtExceptionHandler(new InstallerJDialogUncaughtExceptionHandler(this, noConnectionErrorMessage));
     installerThread.start();
   }
 
diff --git a/app/src/cc/arduino/contributions/packages/ui/ContributionManagerUI.java b/app/src/cc/arduino/contributions/packages/ui/ContributionManagerUI.java
index 717ab1b43..fafc67a5c 100644
--- a/app/src/cc/arduino/contributions/packages/ui/ContributionManagerUI.java
+++ b/app/src/cc/arduino/contributions/packages/ui/ContributionManagerUI.java
@@ -78,7 +78,7 @@ public class ContributionManagerUI extends InstallerJDialog {
   }
 
   public ContributionManagerUI(Frame parent) {
-    super(parent, _("Boards Manager"), Dialog.ModalityType.APPLICATION_MODAL);
+    super(parent, _("Boards Manager"), Dialog.ModalityType.APPLICATION_MODAL, _("No internet connection available, the list of available boards is not complete. You will be able to manage only the boards you've already installed."));
   }
 
   public void setIndexer(ContributionsIndexer indexer) {
@@ -145,7 +145,7 @@ public class ContributionManagerUI extends InstallerJDialog {
         }
       }
     });
-    installerThread.setUncaughtExceptionHandler(new InstallerJDialogUncaughtExceptionHandler(this));
+    installerThread.setUncaughtExceptionHandler(new InstallerJDialogUncaughtExceptionHandler(this, noConnectionErrorMessage));
     installerThread.start();
   }
 
@@ -168,7 +168,7 @@ public class ContributionManagerUI extends InstallerJDialog {
         }
       }
     });
-    installerThread.setUncaughtExceptionHandler(new InstallerJDialogUncaughtExceptionHandler(this));
+    installerThread.setUncaughtExceptionHandler(new InstallerJDialogUncaughtExceptionHandler(this, noConnectionErrorMessage));
     installerThread.start();
   }
 
@@ -194,7 +194,7 @@ public class ContributionManagerUI extends InstallerJDialog {
         }
       }
     });
-    installerThread.setUncaughtExceptionHandler(new InstallerJDialogUncaughtExceptionHandler(this));
+    installerThread.setUncaughtExceptionHandler(new InstallerJDialogUncaughtExceptionHandler(this, noConnectionErrorMessage));
     installerThread.start();
   }
 
diff --git a/app/src/cc/arduino/contributions/packages/ui/InstallerJDialogUncaughtExceptionHandler.java b/app/src/cc/arduino/contributions/packages/ui/InstallerJDialogUncaughtExceptionHandler.java
index 01a80be0f..a5007fe41 100644
--- a/app/src/cc/arduino/contributions/packages/ui/InstallerJDialogUncaughtExceptionHandler.java
+++ b/app/src/cc/arduino/contributions/packages/ui/InstallerJDialogUncaughtExceptionHandler.java
@@ -9,21 +9,28 @@ import static processing.app.I18n._;
 public class InstallerJDialogUncaughtExceptionHandler implements Thread.UncaughtExceptionHandler {
 
   private final InstallerJDialog parent;
+  private final String connectionErrorMessage;
 
-  public InstallerJDialogUncaughtExceptionHandler(InstallerJDialog parent) {
+  public InstallerJDialogUncaughtExceptionHandler(InstallerJDialog parent, String connectionErrorMessage) {
     this.parent = parent;
+    this.connectionErrorMessage = connectionErrorMessage;
   }
 
   @Override
   public void uncaughtException(Thread t, final Throwable e) {
+    String errorMessage = _(e.getMessage().substring(e.getMessage().indexOf(":") + 2));
+    if (errorMessage.startsWith("Error downloading")) {
+      errorMessage = connectionErrorMessage;
+    }
+    final String finalErrorMessage = errorMessage;
     SwingUtilities.invokeLater(new Runnable() {
       @Override
       public void run() {
-        System.err.println(_(e.getMessage().substring(e.getMessage().indexOf(":") + 2)));
+        System.err.println(finalErrorMessage);
         e.printStackTrace();
       }
     });
-    parent.setErrorMessage(_(e.getMessage().substring(e.getMessage().indexOf(":") + 2)));
+    parent.setErrorMessage(finalErrorMessage);
   }
 
 }
diff --git a/app/src/cc/arduino/contributions/ui/InstallerJDialog.java b/app/src/cc/arduino/contributions/ui/InstallerJDialog.java
index de18fe1c4..75619e06a 100644
--- a/app/src/cc/arduino/contributions/ui/InstallerJDialog.java
+++ b/app/src/cc/arduino/contributions/ui/InstallerJDialog.java
@@ -58,6 +58,7 @@ public abstract class InstallerJDialog<T> extends JDialog {
   // Currently selected category and filters
   protected Predicate<T> categoryFilter;
   protected String[] filters;
+  protected final String noConnectionErrorMessage;
 
   // Real contribution table
   protected JTable contribTable;
@@ -79,9 +80,9 @@ public abstract class InstallerJDialog<T> extends JDialog {
 
   protected InstallerTableCell cellEditor;
 
-  public InstallerJDialog(Frame parent, String title,
-                          ModalityType applicationModal) {
+  public InstallerJDialog(Frame parent, String title, ModalityType applicationModal, String noConnectionErrorMessage) {
     super(parent, title, applicationModal);
+    this.noConnectionErrorMessage = noConnectionErrorMessage;
 
     setResizable(true);
 
@@ -218,7 +219,7 @@ public abstract class InstallerJDialog<T> extends JDialog {
   }
 
   public void setErrorMessage(String message) {
-    errorMessage.setText(message);
+    errorMessage.setText("<html><body>" + message + "</body></html>");
     errorMessageBox.setVisible(true);
   }