The problem started occurring a couple of weeks ago (I guess with the latest Norton/Thunderbird updates). The program runs fine however the bottom progress pane is stuck on "message downloading" and won't allow any messages to be downloaded. restarting seems to allow it a couple of runs before it gets stuck again and disabling the Email scanner seems to solve it completely, however since it's downloading from a non SSL POP3 server, I'd prefer to keep the mail scanner on.
Thanks for helping!
Norton security 22.5.4.24 Incoming port POP 3 110 Outgoing port STMP 25
Windows 7 ultimate 64bit sp1