vpn through isa server with sp1

My VPN is only allowing users to connect, see all the servers, but when you try 
to zoom in to the file details under the server, user is being asked username 
and password (but not domain name ) again, and doesn't matter which user you 
use, you never get pass the password/username windows!!!
 
If the user has admin right, then he can get through.
 
Any input is much appreciated.
 
I have a simple one domain network with ISA server front end and all other MS 
server behind the firewall.

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