trying to call membership to get users email and then add to MailMessage class?

hi,
I am trying to call Membership Table and get the User Email address based
on value of QueryString- I then add the email to Mail Message class.

QueryString
http://xxxxxxxxxxxxxxxxxxxxxxxx?Cell=1db23659-aacb-44d9-b028-bf88f27a65ea

Tried it this way but it does not execute

        MembershipUser user = Membership.GetUser(Cell);                         string name = user.UserName;
                        mail.To.Add(user.Email);

Mail Message Class ...