Index: trunk/src/org/openstreetmap/josm/actions/UpdateDataAction.java
===================================================================
--- trunk/src/org/openstreetmap/josm/actions/UpdateDataAction.java	(revision 1463)
+++ trunk/src/org/openstreetmap/josm/actions/UpdateDataAction.java	(revision 1464)
@@ -10,4 +10,6 @@
 import java.util.ArrayList;
 import java.util.List;
+
+import javax.swing.JOptionPane;
 
 import org.openstreetmap.josm.Main;
@@ -67,4 +69,10 @@
         }
 
+        if(bboxCount == 0) {
+            JOptionPane.showMessageDialog(Main.parent,
+                        tr("No data to update found. Have you already opened or downloaded a data layer?"));
+                return;
+        }
+        
         int result = new ExtendedDialog(Main.parent,
                 tr("Update Data"),