I played through as part of the Dawnguard. Upon entering the Soul Cairn for the first time, I had Serana turn me into a Vampire Lord. After acquiring the elder scroll and leaving the Soul Cairn, the homies and Fort Dawnguard were [censored]ing about me being a vampire, so I cured myself. I proceeded through the questline until I killed Lord Harkon. Now I want to re-enter the Soul Cairn to tell Valerica that Harkon is dead. When I aproach the portal to the Soul Cairn it doesn't let me in and starts draining my health. So I had Serana turn me back into a Vampire Lord while in Velerica's study and tried to enter again. Same thing. No teleport, drains health. I try transforming into a Vampire Lord and entering... no luck.

I'm playing on 360, so no console...

Try having her turn you into a VL on the balcony and then enter the Soul Cairn.

That worked! Thanks Zaied.