SID files sharing

Hi

I work in a school and we have two networks curriculum domain and the admin domain. Untill today i've been able to just add the admin users to curriculum folder permission to allow them access. I've come back from holiday and admin staff no longer have access. I checked the sharing a security and instead of it saying "admin 13" it just has unknown account followed by the SID, I am however able to remote into the curriculum server from an admin machine. Is this an easy one to sort out? The curriculum server is running 2003 and the admin is running 2008 if that would make any difference.

Any help would be great

When you say two networks do you mean two domains, two vlans etc?
If it is only showing the sid the server cannot contact the domain to lookup the user name / group associated with the sid, or the user / group was deleted.

I would make sure it is contacting the domain correctly or look into any cross domain trust issues.

Normally when an account has been deleted it displays the SID instead of the username .

As its a domain trust , i would assume there's either a Trust linkage problem , firewall issue or an AD malfunction ?

Have you rebooted both servers and checked all event logs ?