To me, this sure looks like a GB2 bug, and I'd submit a BugTracker for it
It looks like the problem is triggered because GB2 wants to mail, but can't find a mailbox.
Try adding a <Mailboxes> element to whatever profile you're using.
That might fix you up and have you on your way. But, even if it does, please submit a BugTracker to have this looked at. If not, the problem will be around forever.