Files different from server.

Hi, I try to join a MP game but it just says "Files different from the server"
What should I do? Please help :P

You never even said if you're using Steam or a private version. We're not mind readers bro. But the error means exactly what it says: Your files or the server's files are either outdated or updated while the other wasn't. If you're on Steam, just use their option to verify all the files.