I downloaded the DLC last night and resumed my game. Joined the Dawnguard, freed Serana and took here across the bridge to the keep.... and nothing. The guard will not open the portcullis. I speak to Serana and she confirms this is here home. Apparently after looking on the net she is supposed to say something on her own as we cross the bridge and its not happening.

Is there any fix for this or have I just gotten a completely non-functional DLC?

I am sort of dreading having to start a new game to try to test out if its some problem with the fact that my old game was started before the DLC was installed.

If you have already discovered Castle Volkihar, then after speaking to Serana for the first time when she is released from the sarcophagus she will automatically initiate dialogue with you that normally occurs shortly after arriving at Castle Volkihar.

Visiting Castle Volkihar prior to finding Serana: In this case, you will need to load a prior save game, before visiting the castle and find Serana first.

See here too: http://www.youtube.com/watch?v=MgxGT6_49G0

or

you might try the wooden plate glitch where you drop a wooden plate, pick it up and hold it at eye level and then rush forward to get through the door. !!!!!

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btw you DLC is full functional, this is a game glitch and happens some times.

Thank you so much!

I hope, it helps you out....