man thats the same exact thing that happens to me. i also own a 6600gt! i wonder if its a video card issue ,like in the new drivers, or mabey something to do with the newpatch?? man it plays on mine for hours at a time, but at random times and various diff days it just shuts the game down and sends me back to the desktop! hmmm i have amd athlon 64 3200+ with 6600gt but mines the 128meg version. so we have a few things in common with our systems! i wonder what it could be. i know , this its irritating as hell! lol.