Delay when unlocking XP workstation

I am experiencing a delay of approx 1-2 min when I unlock one of my XP SP2 workstations. The delay does not exist upon initial boot up or upon re-boot. This is NOT spyware, a virus, or a start-up program issue, and I have even changed the Winlogon/DcacheMinInterval timeout in the registry (WAY back to NT 4). Does anyone have any idea why this would be happening and what I could do to fix it? Thank you.