if i wanna join a server, it doesn't work because there is an error message which says: "Your CD-key is not valid" can anybody help me?
..And sorry for bad english

No, not necessarily. I've had this happen to me as well. I just reinstalled the game, since I had all the patches and such on my disk already. In my case (and this happened to a lot of people already), the registry got a tiny bit twisted or something, which results in the game giving you this message.Sacher wrote:it means you have a cracked game
