In the Rising at Dawn quest where you can cure vampirism, i first spoke to the Falion and bringed him a filled Black Soul Gem. Then he said that i must meet him at dawn at the Black Marsh. But i missed him! The next objection in the quest is to speak to the Falion again, but now he wont speak to me about curing vampirism.

Any ideas how to cure me? Ive been a vampire 50 days...

Try waiting until night fall again when he's at the circle in the marsh?

He goes there every night around 2:00am and that is the only place he'll do the cure.