I'm also getting this problem. At first I thought it was when I used the keyboard to fire weapons (eg. 1 - 8 key shortcuts), but then I got further on the "Into the fire" mission, and it kept crashing when just using the mouse. This seems to only happen during combat, and my settings are on full using a Radeon HD5770\Win 7 32bit. I'm going to try to tone my settings down a little to see if that helps.