Go post your problem in the support section or this post(Might as well) and you might get an answer on how to fix it instead of jumping to calling out TWI. Not everyone has this error so it might be something unique to your PC. Give us your hardware specs and your Killing Floor log.
Your log file is located in your game dictionary(I'm on XP so this is what is is for me, may be different for OS Vista or 7): DriveLetter:/Program Files/Steam/Steamapps/common/Killingfloor/system. Give us the contents of your Killing floor log file. Don't worry, it does not contain personal information, just information about KF booting up.