#2 - April 30, 2009, 2:11 a.m.
If you are receiving the In-Use message when you attempt to use the Authentication Key that means it has already been claimed and is no longer valid. To take a bit from our Authentication Key FAQ:
Q u o t e:
What does it mean if my Authentication Key has already been claimed?
If you are receiving this message, it indicates that this Authentication Key has already been used to create or upgrade a World of Warcraft Account. Once an account has been created or upgraded using a key, that key is no longer valid.
It is possible you could have received this message on accident. A possible cause could be a mistyped key. Several characters that are commonly mistaken for one another are: 2 and Z, 8 and B, and 6 and G. Please recheck each character entered in step two to make sure the authentication key is entered correctly.
Once an account has been created or upgraded using a key, that key is no longer valid. If you are still receiving the message then I would recommend attempting to return it to the place of purchase. Just as if the game were missing a disk or the instruction manual, a copy of the game that has a bad Authentication Key is defective. The easiest and fastest solution to this issue is an exchange through the place of purchase. Explain the situation of the key being used previously and attempt to have exchanged for an Authentication Key that is not in use.
For more information regarding authentication keys, please visit our Authentication Key Frequently Asked Questions page at:
http://us.blizzard.com/support/article.xml?articleId=20499.