Well, if you can get me any more tips on where it crashes, i might tell you the exact cause.
It occurs when going to the map screen. Other than that, I've never found a pattern. It happens in a variety of areas, perhaps one time in twenty, though I haven't been able to reproduce it by deliberately going to and from the screen in rapid succession. I've had situations where I've saved, then very shortly afterwards had a crash, then reloaded, tried again, and had no crash.
I hope you turned logging on, so you will have a baldur.err/baldur.log
Yes, though I'm the first to admit I don't really understand the structure of those files. (Hence my false positive above.) So far as I can see, the map crashes leave no signature in baldur.err. My Baldur.log seems to consist entirely of lines like
CVisibilityMap::AddCharacter : ( 2744, 810 ) #:1441814 R:14
which I don't know how to interpret. Having said that, I don't think I've seen a map crash locally for a little while so (depending on when the .log file is reset - is it ever?) may mean that the record is lost.