Please see the PTR FAQ thread on this forum:
http://forums.worldofwarcraft.com/thread.html?topicId=20126978817&sid=1

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Q u o t e:
Locked characters on the PTR


* Players that have updated their accounts to Wrath of the Lich King within the past few months may not be able to access some characters after copying them to the PTR servers. This includes premade characters.
* If you are receiving the error "Character Locked - Contact Billing" when trying to log into the PTR, you will not be able to access that character during this testing phase.
* Thank you for your interest in participating in the PTR, we hope to see you during the next testing phase.


Please understand that while we would like for you to be able to participate in the PTR, we will be unable to handle issues with locked characters on the PTR on an individual basis.

New threads created regarding locked characters will be deleted.

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