If your geting the following error in your system log do the following.
On your root level PDC emulator domain controller run the command at a command prompt:
net time /setsntp:ntp2.usno.navy.mil /set /y
Then restart the time service.
On all child domain controllers that are the PDC emulator for the domain run the following command:
net time \\ROOT-DC-name /set
Change ROOT-DC-name to your root level domain controller name running the PDC emulator.
Then restart the time service.
Check your system log. You will see confirmations that the local time service is now syncing with the time source.