Are you guys also getting locked out when joining up with a premade group? I used to think it was a bug that I got locked out after doing the instance once (i.e. no bosses the second time the dungeon was assigned), but then I read this post which seems to suggest that you need to group with a "stranger":

http://forums.wow-europe.com/thread....610762&sid=1#5

Anyone know of any info on this issue?