Access permissions being deleted

We are running NT 4.0 with SP6.a on all servers. Most of our clinets are running Windows 2000 professional. We have administrators for different organizations within the network.
These administrators give access permissions to the users in there department.
Since we upgraded most of the administrators to Windows 2000 intermittently administrators would give permissions to someone and then in a few hours or maybe the next day the permissions would be gone, they would have to re-do the permissions for that person.
This is only happening when we use Windows 2000 Professional with Admin tools installed. If you give the permissions from a server we never experience the problem.
Any suggestions