Administrative Shares - No access to enter user name

I have been deploying Windows XP Pro via the new Ghost
Corp Ed. and I have run into 3 instances out of 36 that I
have not been able to, after configuration for the user,
access their machines H/D via an administrative share.
(ie. \\admin\c$)

It prompts for password but give no option to change the
user name to administrator. It gives a grayed out 'Guest'
login and I have no access.

Any ideas that I could check out to resolve these 3
machine issues.

amsmts1