adding user to membership and roles

hi everyone,
its very easy to add users to roles by using the in built controls. but how can add users through customized login controls?. i have tried using

                //MembershipUser m = Membership.CreateUser(name, pass, null);       MembershipUser m = Membership.CreateUser("username", "password@12", "something@e.com");
but it throws an error stating the input provided is wrong. i also tried using all parameters, but then also it throws the same error. 
pls provide some insight into this issue



...