A faulty sprite or similar should cause a CTD in every battle where the sprite or whatever is in use, shouldn't it ? And at least the ones I keep having seem to be entirely indifferent to the exact composition of armies, terrain and weather involved - the only common factor would seem to be that they are after the very first battle of a session.

Army size may be an issue at least in part though. I remember having fought a small series of minor battles with bandits without trouble, then *BAM!* all of sudden a CTD. The longer the game has been running the greater the risk seems to become, which is why I've been assuming it's some sort of "memory overflow" issue. Although whether memory-hogging other programs are running at the same time doesn't seem to affect the CTD rate, merely overall game and loading speed.