I am receiving the same error message. (I don't think the other two replies understand the issue.) When I got the beta key from Amazon last month, I entered it and it was accepted just fine. (I've verified my email address and have only _one_ account w/ Bungie.) (I was in the Alpha and used the same email etc.) But now the error message tells me (and you) that supposedly the key was, in fact, _used successfully_…but for a different account! I sent a customer service request on the 10th but no reply yet. Sent another request today using a different selected question. Rather frustrating, to say the least. I really would like to play in the Beta and just hope Bungie can figure out what the problem is in time for that to happen.