When I try to reactivate my account I get the message "CD-key already in use." What is wrong?
If you have already registered an account, you do not need to enter any CD-key information as you are not creating a new account. When you load the game, leave the CD-key field blank and click okay. Upon doing so, you will be brought to a log on screen at which point you can log onto your account using your old username and password.
Also it is possible that you may have purchased a used copy of the game, in which case you would need to return it to the store you purchased it from for a fresh, unused CD-key.