Based on what you are saying, there are several possibilities.
First thing I'd do is check that the trust relationship between the domains is still in place- If you want to be safe, just re-establish it.
Next, check your NTFS permissions and group memberships. Usually permissions will be assigned to files/folders by adding domain members to a global group. That global group is a member of a local group, and the local group is given permissions to the filesystem. Yeah, I know, seems backwards and stupid, but that is how MS recommends things when you're working across two domains in a forest. If you get rid of the second domain, things become much simpler.
Without knowing your setup and knowing what your network admin did, it's hard to speculate as to a fix. My first question would be what did he do. My next action would be a swift kick to his rump, and then ask why did he not just deactivate the user account, and change passwords on any privledged accounts that the ex-director may have known. No point in monkeying with settings (that I can see- there may be valid ones) when the goal is just to "escort someone out."
How do your users access the files? Do they have a drive mounted? Or do they access a share directly? What errors do they get? Are the errors when the users are browsing to files, or directly trying to access them?
I hope this helps somehow, or inspires an idea. If you can give us more info, though, perhaps we can help you iron a solution out.
PS- I'm looking for a new job right now too, if you're hiring
(ok, halfheartedly, but I am ready to leave my current position)
PSS- :wave: Welcome to Techspot!!! Hope you get your answers, and then stick around! :wave: