MembershipUser.ProviderUserKey.ToString

When I run the following debugging code it writes out credits:0
Dim MembershipUser As MembershipUser = Membership.GetUser()
Dim UID As String = MembershipUser.ProviderUserKey.ToString
SQL = "SELECT SUM(Credits) As Credits FROM Credits WHERE " & _
"DateDiff(m, [DateTime], GETDATE()) < 6 AND [UserID]=@UserID;"
        cmd = New SqlCommand(SQL, Conn)
        cmd.Parameters.Add(New SqlParameter("@UserID", UID))
DataReader = cmd.ExecuteReader()

        If DataReader.HasRows Then
            Do While DataReader.Read
                sCredits = CheckNulls(DataReader("Credits"))
            & ...