What:
Windows Server 2008 R2
Problem:
Clock on domain controller is drifting.
Event ID 12: Time Provider NtpClient: This machine is configured to use
the domain hierarchy to determine its time source, but it is the AD PDC
emulator for the domain at the root of the forest, so there is no
machine above it in the domain hierarchy to use as a time source. It is
recommended that you either configure a reliable time service in the
root domain, or manually configure the AD PDC to synchronize with an
external time source. Otherwise, this machine will function as the
authoritative time source in the domain hierarchy. If an external time
source is not configured or used for this computer, you may choose to
disable the NtpClient.