I just started playing Dawnguard today. I got to the point where Lord Harkon turned me into a vamp. Went through the vamp lord tutorial and lord harkon instructed me to speak to someone in the castle. After I left the chamber where he talks to you and entered the castle itself ALL of the vamps in the place turned on me attempting to kill me. I reloaded and replayed the mission several times nothing I try seems to help.

Does anyone have any idea of what might cause this and how I can fix it?