Okay so im a bit late but I only just read this today read this today
2006-11-22 - Registrations Closed
Registrations for TD are completely closed at the moment. This means you also cannot use your invites. If you still choose to send out an invite, you will only loose the invite and the person will not be able to join.
Accounts are pruned daily. When the user amount drops below the limit, you will be able to sign up again.