This worked for me with call of Duty 4.
This is to fix communication errors in punkbuster that cause you to keep getting kicked.
Read all before trying this!
1. Navigate to C:\Program Files\Activision\Call of Duty 4 - Modern Warfare\pb
2. Delete these files, if present: PnkBstrA.exe, PnkBstrB.exe and PnkBstrK.sys.
3. Navigate to C:\WINDOWS\system32
4. Delete these files, if present: PnkBstrA.exe, PnkBstrB.exe and PnkBstrK.sys.
5. If unable to delete any files, reboot in safe mode by hitting "F8" while rebooting.
6. You should then be able to delete remaining files.
7. Reboot.
8. Go to: Link removed by the admin
9. Download "pbsvc.exe file.
10. Run this file. Choose install and hit next.
11. This will reinstall punkbuster on your system. When it's done re-installing, it will test the install. This takes a few minutes. It should say that it's ok when done.
12. You should not have anymore communication errors in punkbuster.
