I had the exact same problem in COD 4. This fixed it. Here is what Evenbalance suggested to do:
"Note #2: Please get the PB service component installer PBSVC from this URL:
http://www.evenbalance.com/downloads/pbsvc/pbsvc.exe
Save it to your desktop. You will need to start it with Admin rights.
On Windows Vista just being logged in as Admin is not enough. To start the file with Admin rights on Vista, select the PBSVC executable and right click it. Select "Properties", then the "Compatibility" tab. From that tab, check the box labeled "Run this program as an Administrator" and click OK.
Follow the install process and make sure it installs correctly. After that you will be able to play the game without the need of Admin rights. You only need to follow these steps only once (not for every PB supported game and not on each game start).
Please make sure you allow the service files in security software like virus scanners and/or firewalls. You will need to allow/unblock the services PnkBstrA.exe and PnkBstrB.exe from your "C:\Windows\system32\" folder. In case of doubt, manually add both to your firewall's allow list. After the installation process you will only find PnkBstrA, so just make sure this process file is not blocked. Then try playing on a PB enabled server, in case of a kick, check if PnkBstrB was created and unblock it too.
For more information on the PB service components refer to our FAQ:
http://www.evenbalance.com/index.php?page=pbsvcfaq.php"