So now when I have completed the quest on the Dawnguard side, there seems to be no way for me to return to Soul Cairn. When I first entered the Soul Cairn, I choose to do it by becoming a vampire, which I later cured. Now when I try to enter, the life draining effect that happened when I first tried to enter happens again. I tried to enter by becoming a vampire (again), and that still didn't work.
Serana's mother implied that you would be able to enter the SC again even if you didn't become a vampire again (she said something about your soul leaving a mark on the SC or something), but I'm not sure if that's supposed to work or not. However, I'm sure that it should work as vampire, but it doesn't work either.
Does anybody know how I can fix this?