The Windows 2000 Time service may not be able to connect to and external NTP service if run behind Microsoft Proxy with Access Control enabled?

This occurs because the the Windows Time service runs in the local system context.

If you don't want to disable Access Control, you could schedule the following batch file to run once daily:

net stop w32time                              w32tm -once                              net start w32time
NOTE: See tip 2669 ยป How do I configure an authoritative time server in Windows 2000?