I got the same problem since 17 may.... I have 3 cod4 cracked servers online...
I already reinstalled one the servers but that didn't work... And uploading the crack again also didn't work...
Like you said it have nothing to do with Punkbuster.... It's like the server ip is banned on the master servers or something... because when i try to connect it says "key code in use" and the server don't even notice that there is a player trying to connect. But still strange I also tried one of my other ip's (i have 3 ip's) on 2 of that ip's there have never been a cod4 server on, and still same problem.
To bad that my cracked servers have to end this way,, they were pretty popular.
But I think there is no crack who can avoid this.....