The problem proved to be with a particular message which could not be approved,rejected or discarded. I looked at the message and the sender seemed to be a little odd. So, I made the change below to ListAdmin.py and it seemed to work okay, I don't know if this might cause other problems.

Adrian

160c160 < 'sender' : msg.GetSender(),

            'sender'   : strquote(msg.GetSender()),