I will just copy the response i have do on the other thread... you need see this with UBI soft, AMD or EA... could be an error on the code, or the just an error on the server.
Contact UBI soft or and AMD .... this is the type of problem who allways appears at a launch of a game, whatever it is part of a bundle or not.. ( could be the servers who dont work as it should for register the keys. or they was an error with the codes etc), they will correct it for you. I see this type of thing for any games since years. Anyone remember FarCry 1 activation problem ? Ravenshield ? Crysis 1 ? Crysis 2 etc.
Offtly the key is not allready used by someone, but just the server send back this response ... or maybe if it is the case this time, they will just send you a new key.