When I go to Morvunskar (Previously cleared in " a Night to Remember") I follow the marker which leads me up the double set of stone steps,where the portal appears in "a Night to Remember" and there is a chair with the arrow above it but no Master Vampire in sight. Any suggestions?

He should be in an alcove below.
- Go back down the stairs
- Head toward the back rooms
- Turn right
- Kill

I had the same issue and he wasn't there. Not in that alcove either. The quest triggered prematurely because the "captive" hadn't been captured yet. I detailed it http://www.gamesas.com/topic/1401855-dawnguard-side-quest-tips/. I was forced to reload from an earlier save.