[Max-level]

My friend and I came to a disagreement about a play involving this card. He is a Vampire and we understand that there is no "stack" to resolve things. His argument is that since the rules say you can drop a Race/Class at anytime, that he can drop vampire as soon as I play it. I tell him that the curse must resolve before anything else is done and that this is an example of no "stack".
Who's right?