
Do you have steam running?
http://forums.steampowered.com/forums/showthread.php?t=1149028

turn off steam community overlay.
To turn it off, in your steam main window, go to
View > Settings > In-game (tab) > uncheck the community overlay checkbox
I've not had the problem myself, just a spot of googling for you.
it seems like its the steam community overlay, i've found instructions to turn it off:

Do u use riva tuner by any chance i know it caused me some issues with punk buster, i had to uninstall it.



download pbupdate from punkbusters website this will update the game client manually and will solve your issue.

Apparantly it's not just the Steam overlay, it's any overlay that runs with the game. Such as FRAPS, X-Fire, Teamspeak, Ventrilo, Mumble, WMP etc.

punkbuster does sucks at times....


googled it? The most common cause is using overlays, turn them off, run pbsetup to make sure you have the latest version, fixes it everytime for me.