This happened to me, you have to download a certain file that replaces an old one inn you're valve directory. I can't remember where though because someone told me on gamespy. But i'll try to see if i can find the site.
*Edit* The file you need to replace is the woncomm.lst
Now I just need to find the site.
*Edit2* Aha! I found the site.
http://games.ssi.bg/woncomm.lst Copy everything there and paste it on a new text file. Then replace the one in you're valve directory. You will notice that the woncomm.lst that is already in you're valve folder is not a text file, but it automaticly changes it to a .lst file or something like that. You might wanna back up you're old file just incase this doesn't work.