Index: trunk/src/org/openstreetmap/josm/actions/downloadtasks/PostDownloadHandler.java
===================================================================
--- trunk/src/org/openstreetmap/josm/actions/downloadtasks/PostDownloadHandler.java	(revision 5147)
+++ trunk/src/org/openstreetmap/josm/actions/downloadtasks/PostDownloadHandler.java	(revision 5149)
@@ -10,4 +10,5 @@
 
 import javax.swing.JOptionPane;
+import javax.swing.SwingUtilities;
 
 import org.openstreetmap.josm.Main;
@@ -81,16 +82,20 @@
         //
         if (errors.size() == 1) {
-            Object error = errors.iterator().next();
-            if (error instanceof Exception) {
-                ExceptionDialogUtil.explainException((Exception)error);
-                return;
-            }
-            JOptionPane.showMessageDialog(
-                    Main.parent,
-                    error.toString(),
-                    tr("Error during download"),
-                    JOptionPane.ERROR_MESSAGE);
+            final Object error = errors.iterator().next();
+            SwingUtilities.invokeLater(new Runnable() {
+                @Override
+                public void run() {
+                    if (error instanceof Exception) {
+                        ExceptionDialogUtil.explainException((Exception)error);
+                    } else {
+                        JOptionPane.showMessageDialog(
+                                Main.parent,
+                                error.toString(),
+                                tr("Error during download"),
+                                JOptionPane.ERROR_MESSAGE);
+                    }
+                }
+            });
             return;
-
         }
 
@@ -98,5 +103,5 @@
         //
         if (!errors.isEmpty()) {
-            StringBuffer sb = new StringBuffer();
+            final StringBuffer sb = new StringBuffer();
             for (Object error:errors) {
                 if (error instanceof String) {
@@ -109,9 +114,14 @@
             sb.append("</ul></html>");
 
-            JOptionPane.showMessageDialog(
-                    Main.parent,
-                    sb.toString(),
-                    tr("Errors during download"),
-                    JOptionPane.ERROR_MESSAGE);
+            SwingUtilities.invokeLater(new Runnable() {
+                @Override
+                public void run() {
+                    JOptionPane.showMessageDialog(
+                            Main.parent,
+                            sb.toString(),
+                            tr("Errors during download"),
+                            JOptionPane.ERROR_MESSAGE);
+                }
+            });
             return;
         }