Just adding my 2 credits that this CTD has happened to me as well.
Night mission, I had an M-16 grunt spot the alien (grey, was in darkness) and crouch, then my sniper fired a shot (maxed out APs), shot traveled to the grey, stopped at alien for a few seconds, then CTD.
Windows 7 64bit, Core2 Quad (Q9400@2.67Ghz), 4GB RAM, ATI HD 5850 w/1GB (latest drivers via Steam update; Driver Packaging Version 8.961-120405a-137224C-ATI
)