Solved - I followed an advice to delete save files and that fixed the problem. HOWEVER what caused the error was not a recent save but one of the older ones! (Weird)
I got this same problem - line 1957 - when I start up ToB and try to load a game!
Not sure if I got the problem before or after I started to dl mods for planescape yesterday, but I will delete them all just in case.
Emptying chaches and temps seem a good suggestion to.
I can add that I DO NOT run any anti-virus program. Vista is unhappy with this but I found them more than a little bit annoying.