Call of Duty: Modern Warfare 2 Message Board  

Sounds like a corrupt/missing file to me. I would try re-installing. Just make sure you backup your game saves (although an uninstall should either ask you what you want to do with them, or simply leave them in-place without asking you).

Thanks for the help everyone, optimal setting did the trick and I finally beat the game

But what a crappy programming, lots of errors and bugs