Can't add roles to a user

Hello,
Why I can't add a role to a user, I am getting this error "'Value of type 'System.Web.Security.MembershipUser' cannot be converted to '1-dimensional array of String'."

Dim UName As MembershipUser
        UName = Membership.GetUser()
        Roles.AddUsersToRole(UName, "Administrator")

I also have the same error when manually using the username such as,
        Roles.AddUsersToRole("Bob", "Administrator")





-imperialx

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