The issues related to logging in to the North American PC/Mac megaserver have been resolved at this time. If you continue to experience difficulties at login, please restart your client. Thank you for your patience!
I had an unresponsive NPC for a quest. Relogging fixed that. If this is a quest NPC, drop the quest & retake it to see if that fixes your error. I have not had an unknown error since Early Access, so I am not sure if the two are related.