I'm trying to get cured of the annoyance of being a vampire; but the witch, Melisande, is giving me problems. She asked for five ingredients to make a potion. She took four of them without a problem, but refuses to take my bloodgrass. I've closed four Gates of Oblivian to try different sources, and even bought some from a shop in Imperial City. The witch will take none of it. Does anyone know what the problem is here?

My guess is that you are playing the game on a PS3. If so, there is no solution. It is a well-documented bug that Bethesda never fixed.

No-o-o-o-o-o! That is so frustrating! You are so right, SubRosa, I'm on a PS3. Thanks for the information.