I had that problem a while back, it was so annoying I ended up uninstalling the game for a few months out of frustration. I reinstalled it today though, and managed to fix the problem.
The Dual core optimizer didn't work for me, I too have dual core AMD processors, but disabling multicore in the graphics options has gotten rid of the issue almost entirely, and since I was running the game on fairly low settings anyway I haven't noticed a drop in performance at all. In fact, it seems to have gotten rid of some of the choppiness I was experiencing frame rate wise. The game still does occasionally crash, but I was playing for about 6 hours solid today with no problems, whereas before I could only play for about 15 minutes.
Hope this helps!
