security: cannot add domain groups "Unable to look up user names for display"

[Vincent Fox]

I'm trying to loosen security on a particular folder.
What I would think would work, which is to go into Security
for that folder, and add domain users to have full control
on that folder, doesn't work. I can pick the domain name
and then pick the Domain Users group. However when I go
to add it, it give "Unable to look up user names for display".
Is this a config issue I have overlooked?

Samba 2.2.1a as a PDC
Win2K Pro SP2 clients