Index: /trunk/autoquest-core-events/src/main/java/de/ugoe/cs/autoquest/eventcore/guimodel/GUIModel.java
===================================================================
--- /trunk/autoquest-core-events/src/main/java/de/ugoe/cs/autoquest/eventcore/guimodel/GUIModel.java	(revision 1282)
+++ /trunk/autoquest-core-events/src/main/java/de/ugoe/cs/autoquest/eventcore/guimodel/GUIModel.java	(revision 1283)
@@ -428,5 +428,8 @@
         // check if both nodes have the same parent
         IGUIElement parentElement = guiElement1.getParent();
-        if (parentElement != null && !parentElement.equals(guiElement2.getParent())) {
+        boolean sameParent = (parentElement != null) ?
+            parentElement.equals(guiElement2.getParent()) : (guiElement2.getParent() == null);
+            
+        if (!sameParent) {
             throw new IllegalArgumentException("can only merge nodes with the same parent");
         }
@@ -434,4 +437,9 @@
         // get the TreeNode of the parent of the GUI elements
         TreeNode parent = findNode(parentElement);
+        
+        if ((parent == null) && (parentElement == null)) {
+            // merging root nodes. The parent is the root node of the GUI element tree
+            parent = root;
+        }
 
         // get the TreeNodes for both GUI elements