Set up Clustering !!!!!!!!!

Anyone know why I got this exeption when I set up clustering. "java.io.IOException: Server returned HTTP response code: 401 for URL: http://cm-web1.cen.com:4504/crx/config/cluster.jsp". I try to join that url to the master author then I got that exeption.

I follow this url http://dev.day.com/docs/en/crx/current/administering/cluster.html  instruction.

Thanks,

Jenny