You did put the .pk3 file in the "main" folder and not the .zip file that the map would have come in ?? Make sure all mods/maps/whatever are .pk3 files.
Ok, well, basically, I have no idea, I've never had the problem before. Only problems I've had are connection to server times out, thats about it. What I'll do is move this thread to General Discussion and hopefully someone there will be able to help you. There's a great deal of helpful people in there, I'm sure someone will figure out your problem. Good luck mate, sorry I couldnt have been more helpful.