CUPS access via web interface

Hi List; I want to use the cups web interface to manage my printers however when I go to http://localhost:631 and select 'Manage Printers' or 'Administration' I am prompted for a username/password. with this message: Enter the username and password for "CUPS" at http://localhost:631 I've entered the local root username/password and my username/password but neither work. Anyone know what I'm missing ? Thanks in advance for your help... /Kevin