Hello and thank you!

I have a block where I sign up a user from Facebook. What I want is when the user already has a local account on the site I want this error message like: You are already registrered on this site" and I want the user to be redirected to the View of that page. Problem is in backend:

I'm at the moment using RedirectToaction("Index",model); I dont really have to send further my model but anyways: The problem is that  when i return this I get redirected to the block wich isnt pretty in the view. This means I'm not able to get to the sign in page but the block view. 

Any ideas on what I can do here?

//Alex