So I'm level 30, just started Waking Nightmare quest. I follow Erandur into the Nightcaller Temple, and we make it down the stairs. He tells me we need to go the library to retrieve a book and the quest marker tells me to 'follow Erandur to library', but Erandur just stands on the stairs. He doesn't move. I've tried restarting the game, talking to him, I've even tried killing him but since he's a quest character he won't die. He just stands there! Any ideas how to get around this bug? He has the key to the library but I can't pickpocket it from him, and since the library is locked with a key I can't lockpick it either. Help!

I fixed this problem by continuously running into him to "push" him up the stairs. As soon as he reaches the top he should start walking again.

Same here. I also shouted him up. Once at the top he resumed his approach to the library.

I shouted him up and it worked Thanks guys!