[Bug] Fade out Stuck on dual class change start

[Jumbo]

I was doing cleric class quest and then tried to enter just after another cleric. I got the error message "only one player can blablabla", and I didnt enter the quest area. However, I got the fade effect permanently and was therefore stuck with a black screen for the rest of the game. Pretty serious bug it seems, although it is a rare thing to happen.

EDIT: I was dwarven cleric and the other player was normal cleric.
This bug happened again in a strange way: After I completed the quest I left the quest area, and when he activated it I got pitch black screen. At the same time, the soldiers from my quest hadn't despawned so he had extra soldiers for his quest.