Comment 2 for bug 1199984

It seems a bit odd but this fixes it.

 $ bzr cdiff
=== modified file 'DistUpgrade/DistUpgradeFetcher.py'
--- DistUpgrade/DistUpgradeFetcher.py 2013-01-15 15:51:10 +0000
+++ DistUpgrade/DistUpgradeFetcher.py 2013-08-21 23:49:21 +0000
@@ -47,7 +47,7 @@
         self.window_main = parent

     def error(self, summary, message):
- return error(self.window_main, summary, message)
+ return error(self.window_main.window_main, summary, message)

     def runDistUpgrader(self):
         inhibit_sleep()