When I play Call of Duty 2 for 5 minutes or so, PunkBuster throws me away from the server and it says 'Restriction Service Communication Failure: PnkBstrB.exe initialization failed'.
If you have PunkBuster problems, download the setup and install it by removing the old version. You don't need to worry because the setup will detect the version installed in your computer and it will remove it by installing the new one.