Big Delay trying to add new ACLs to files

On one of the domains in my new 2003 forest, no matter which server or
workstation you try this upon, whenever you want to add more ACL permissions
to a file or folder , after you click the "Add" button, it takes about 12
seconds before it presents you with the dialog box to select users groups of
computers. At every other domian in the forest, the action is instantaneous
instead. All these servers and workstations are 2.8-3.4GHz, gigabit server
backbone with switched 100Mbps to all workstations.

There is virtually nothing else running on any of the machines at the time
since this is a brand new freshly deployed network.

Any clues to help troubleshoot this annoying delay? DNS is up and
configured correctly, everything else that has to do with DNS lookups is
lightning fast. Any other kind of network traffic between these machines is
also lightning quick too.