Lockups only when Shadows are ON

[Drax86]

Hey all,

This problem seems similar to some described in the dual/quad core threads, but it only happens when I enable Shadows.

Every 20-60 seconds roughly, the game locks up for about 5-10 seconds at time, Windows gives me some video card driver error, and the game goes black until I Alt+TAB out and back in.

I am running it with all other graphics settings at max, and at 1370 x 768 Full Screen, although the same thing will happen in Windowed mode as well. If I turn Shadows off I have no problems what so ever.

I've tried a few of the suggestions for the dual/quad core threads which didn't help.

Any suggestions?

System Specs:

Windows 7 64bit
8GB of RAM
AMD Phenom II 2.6GHz Quad Core
ATI Radeon HD 4870 512MB DDR5
All Drivers and DirectX are up to date