It IS registered; with an account that's for some reason different than this one.
If this is the case, contact the helpdesk by clicking on the link at the top of the forums, and have the helpdesk consolidate your account(s). Once this is done:
1) You won't be bothered by this issue again.
2) People will listen to you as a registered user and not ignore you because of suspicious account activity or suspicion of piracy.