diff -r 3d7fa2257b24 -r 85ca4fa0720b dialogs/BlockPreviewDialog.py
--- a/dialogs/BlockPreviewDialog.py	Tue Sep 10 10:35:18 2013 +0200
+++ b/dialogs/BlockPreviewDialog.py	Tue Sep 10 10:36:44 2013 +0200
@@ -177,7 +177,7 @@
         
         # Add POU name to variable list if POU is a function 
         returntype = self.Controller.GetEditedElementInterfaceReturnType(
-                                                            self.TagName)
+                                                            self.TagName)[0]
         if returntype is not None:
             self.VariableList[
                 self.Controller.GetEditedElementName(self.TagName)] = \