It may not be related but make sure to install the latest DirectX (9 or better) & make sure that you are using the latest video drivers. Drivers that are bundled with your video card are in most cases outdated and usually the latest games do not even work...
It is just bad checking on the game developer part, they should check if their games work on older configurations and if it does not that it gives hints how to solve possible problems... that would be a perfect world...
As for the default.cfg problem have a look here:
http://www.google.com/search?hl=en&l...all+of+duty%22
Is is related to a missing directory... again a game developer ****up on checking if the game was installed correctly or not...