Hye i need to provide single sign on place  to the asp.net and DNN.

Asp.net application is Asp.net login control and aspntdb database for roles and users authetication and authorization.In short Form based authentication is there.
Now mostly in SSO on same domains application, you try to have same machine key, and name of the cookie in web.config and then you can have SSO.
This works fi9 when i tried this with two asp.net web apps but this is certainely not working with DNN and asp.net application.
Reason can be firsty  in Roles are not enabled i mean in web.config and on asp.net i have a role with name basic which is allowed to visit secured aeras.
And secondly DNN does not implement the roles and user authentication the web app is doing.
I mean i even tried to have same cookie name and machine key in both application, i was getting error in webapp that aspnetdb aleady exist and all.
 
So can any one help me with that.i mean with code examples and all.
 
And 2nd issue could be if i make new role and user in DNN, how itwill be mirrored in webapp database