I am also having this issue with a Steam key. I had tried to enter it just as the activation system started to buckle. Apparently, it recognized the key, but the system failed before it could correctly attach it to my account. If it would help, I can PM you the key, once the mail system is working again.
I also have the same problem. After not being able to finish the registering process a couple of times, now every time I try to enter my key I get the "This product key is already active, it cannot be used again" error.
*edit* My account info finally updated. However, because I couldn't finish the billing info my subscription listed is currently a game card.