Setting a default User Role

Hello all,
I am attempting to set up a web application for which when users register their default role is does not permitt full access. So far I have attempted the following and it doesn't work
During and at the completion of the registration (psuedocode)
get the user name
check role
if the user is not assigned to a role
assign default role
end if.
if(User.IsInRole("Default") == false)
{
Role.AddUser("CreateUserWizard.UserName","Default")

}
This does not seem to work. Does anyone have any suggestions
...