Hi,
a few days ago, a shocking news came out:
Evenbalance full stopped the support for ET and RtCW.
To enable playing on PB secured server, the neccessary etkey files is no longer generated.
Old player will not have any problems, but:
New player are unable to join such a server.

For this reason I foundet http://etkey.org , where everyine can simply generate a new etkey file. Additional to this you can find the actual Punkbuster client files for windows and linux there.