Hi, i wonder if anyone can suggest a course of action. I've come across a completely unexpected and game breaking issue. I've scoured goggle and i can't find a similar situation anywhere.

During the Bloodline main quest for Dawnguard as i'm bringing Serana home to the castle, the second i walk under the archway into the main hall Serana becomes hostile to everyone in the castle and vice versa. If i stand back by the door she'll walk in and do all of her dialogue etc with no problems, it only happens as soon as i (the player) cross that particular threshhold. As soon as the vampires knock Serana down Harkon will begin his dialogue, when she gets back up they attack her again and so on. I've tried going along with Harkons training and seeing if it works itself out but once finished i go back to the hall to find Serana still trying to attack people but they all just ignore her.

I've also tried removing any mods i can think of that might be effecting Serana or vampires in general but it makes no difference.

Strangely when i load up a previous save game and go to the same point in the quest, everything works as it should. So it seems tied to this particular playthrough but i'm at a complete loss as to what could be causing it or how to solve it.

Any help or suggestions would be greatfully received, as the whole point of this playthrough was to start over to play Dawnguard from the beginning.