I'm having a similiar problem. For me the game freezes, the the screen flickers and I get a DivX not found error message. This sometime happens 5 times in 1 hour, or never in a 5 hour game span. Never quite figured out what it is.. But my thoughts are that i spent to much on my GPU and not enough on my MB/CPU. I think I'm bottle necking my system.

I currently run a...
AMD Phenom II X4 955 ~ 3.2Ghz on a ASUS M4A785-M Motherboard > Windows 7
AMD Radeon HD 6800 serious Graphic Card.

If anyone knows how to fix these issues.. do tell!