Are you using an nvidia video card?
EDIT: PB thinks you're running something suspicious while playing the game. It could be a hack or it could be a legitimate piece of software that it thinks is a hack. If you have a hack or cheat running, get rid of it and try again. If you don't have one running, you need to identify what is running that's making PB think you're cheating. I can't really help you much beyond that. If no one can help you, maybe you can try submitting a web ticket to PB.
Check out the PB support site for COD2 if you haven't already:
http://evenbalance.com/index.php?page=support-cod2.phpThere's a link to the web ticket system right there.
Good luck.