Adding user to group requires Server (svc) restart te enable user permissions

Hi

I've got a windows2000server member server (of an NT4
domain). We have a group (on that server) called "central"
which I add domain users to - to enable certain fileshares
to become available.

I've discovered today that just adding/removing a user
to/from the "central" group no longer (its been a while
since i had to do this) automatically enables that user on
the shares with "central" allowed on them.

So far the only way i can get the user enabled is to
restart the Server service, which causes all sorts of
problems for active users.

Has anyone heard of this problem? Any ideas?

There are no obvious events in the logs (System,
application and Security) relating to these security
failures or the Server service.

Thanks,

Wayne.