It is most likely that the issued cd-key has expired or it is not good at all. As I can see the game dates back to 2003 so Internet activation wasn't a good approach at that time. This leaves the offline activation which in your case is not working. There isn't much to do about it except the fact that you will need to contact the supplier of the CD-key (publisher/official developer) and state the problem you have. They will sure help you with everything you a new CD-key.