Do you have the latest graphics drivers installed? In my experience with AMD drivers they might sometimes **** up. Also could you be more detailed of what kind of system you are running this game on?

Of-topic:
Also it is a bad idea to run this game on max settings. You might not notice much lag but in a place with lots of fire traps your framerate will go down big time since that is still not optimized. I have a EVGA GTX 570 HD btw which outperforms your graphics card and even I cannot handle max settings in for example Firestorm Citadel. This game is badly optimized.