Das war die Antwort vom PB support:
If you are being kicked for a "Communication Failure" it is likely that something on your computer is preventing the PnkBstr services from communicating with each other.
A common cause for this is a security or anti-virus program. McAfee and other popular security/firewall programs need to be told to allow the PnkBstrA and PnkBstrB services to run without restriction (even if you turn them off while playing; the service files are located in "C:\Windows\System32" or "C:\Windows\SysWOW64\"). Until you locate and remove the restrictions on PnkBstrA and B, you will continue to be kicked for this. DO NOT remove those files! E.g. if you are using a software firewall you will need to unblock/allow them.
If you've never manually installed the PunkBuster services, you might want to try that as well. Download the service installer from
http://www.evenbalance.com/downloads/pbsvc/pbsvc.exe and run it. You might also want to reinstall the services using this tool.