The problem is that even though you kicked him from group, you didn't kick him from the instance, so it still has 12 people inside. So far as I know, there's no way to actually fix this, short of having the person come back or remaking the instance. I believe after a certain amount of time (half an hour possibly?) the game will completely remove that player from everything, at which point you'd be able to bring in a 12th.
Originally Posted by Framdoro
Steam: Sneakeh Snake[/CENTER]