How to overcome "You cannot enter another instance of this map yet"?

I'm on the quest The End of Salvarola and am attempting to go up the elevator to the throne room. I was grouped with a friend who got the message in the title while I was able to enter (see this related forum post), so we split up which kicked me out of the instance. I re-entered but the quest was messed up (the NPCs were acting like they were on the first step, but I was on the second) so I left the instance again and reset the quest. Now when I try to enter (still solo) I'm constantly getting the same error message that my groupmate originally did. How can I fix this?