It happens many times that the game crashes when you are using some units (
Ents, Balrogs, spiders and others ...) if you solve it in a battle instead of autoresolve.
This happens mainly in new hardware/software.
You could try to autoresolve, just to check if this is the bug (Save earlier so no matter if you are defeated), in this case there is a lot of information on the bug but unfortunately no solution by now except not including these units in the battle.
http://www.twcenter.net/forums/showt...wolves-crashes