Punkbuster no longer supports CoD4, when you go to download it CoD4 is no longer in the list. Follow this guide to install it.
Download PB from here http://www.evenbalance.com/index.php?page=pbsetup.php
Copy pbsetup to a location on your hard drive run it once and let it update if needs be, close pbsetup
Download pbgame.zip from here http://www.pingperfect.com/cod4/pbgame.zip
Overwrite pbgame.htm where you have put pbsetup.exe with the one you just downloaded
Run as normal.
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