The cd-key is case sensitive, and you include the dashes. Be careful not to mix up "O" and "0", "I" and "1" and "B" and "8", and one player even typed a "1" instead of "f". My cd-key is a little hard to read because the center CD mounting prongs distort the numbers and letters.

There is a small possibility that your cd-key is not in Activision's online database. In that case, I think you have to request an exchange of your game through Activision. It's a pain, but I don't know any other way except try to get an exchange through the retailer where you bought it, and that usually has to be done within 30 days of purchase.