Getting the username value from the create user wizard

 Hi,
 i have a create user wizard and i would like to get the username text value from the textbox in the "Username" field and save the value in another table, heres the query i used to get the value from the username textbox:
// Get the UserId of the just-added user
        MembershipUser newUser = Membership.GetUser(Registration.UserName);
        Guid newUserId = (Guid)newUser.ProviderUserKey;
but when i go to create a new account using the create user wizard, i get this error:
No mapping exists from object type Sysem.Web.Security.MembershipUser to a known managed provider native type.
Does anyone know what this means? Or how i could get the username from the username textbox?
Thanks.
 
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