Vampire Lord Questline Broken

[Booduh]

I'm attempting to play through the vampire lord Dawnguard storyline, and every time I tell Lord Harkon I want to become a vampire, he bites me, the screen goes red and fades to black, then I come back glowing blue standing in front of him. Harkon just stands in front of me in VL form, and neither of us can move. Can you help?

 

I've tried clean saves, disabling all my mods, and changing to a vanilla race, and it has no effect. I've even tried the Unofficial Dawnguard Patch mod. Still nothing.