Evenbalance had a problem with their implementation on the fairer platform a few days ago. Solution from Aspyr's support team:
We were given the following to try directly from the folks at PunkBuster. It worked for us.
Download the following file:
http://web1.evenbalance.com/downloads/cod4/mc002301.mac
After the file is downloaded place it into the install path
>pb/dll folder.
Let us know if this fixes things for you.