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When the Windows Time Service (W32Time) synchronizes with a primary domain controller, the following events are logged in a System log that resides on a virtualized domain controller. The virtualized domain controller is running in a guest operating system on a host server that is running Windows Server 2008 with Hyper-V.
Event Type: Warning Event Source: W32Time Event Category: None Event ID: 24 Date: Date Time: Time User: N/A Computer: ComputerName Description: Time Provider NtpClient: No valid response has been received from domain controller Yourpdc.forestroot.com after 8 attempts to contact it. This domain controller will be discarded as a time source and NtpClient will attempt to discover a new domain controller from which to synchronize.
Event Type: Error Event Source: W32Time Event Category: None Event ID: 29 Date: Date Time: Time User: N/A Computer: ComputerName Description: The time provider NtpClient is configured to acquire time from one or more time sources, however none of the sources are currently accessible. No attempt to contact a source will be made for 15 minutes. NtpClient has no source of accurate time. For more information, see Help and Support Center at http://support.microsoft.com.
Event Type: Information Event Source: W32Time Event Category: None Event ID: 38 Date: Date Time: Time User: N/A Computer: ComputerName Description: The time provider NtpClient cannot reach or is currently receiving invalid time data from Yourpdc.forestroot.com.
If you enable Windows Time Services Debug logging on the domain controller, information that resembles the following is logged in the Debug log:
149040 14:15:14.2970940s - Logging information: The time service is now synchronizing the system time with the time source VM IC Time Synchronization provider.
http://support.microsoft.com/?kbid=976924
Read the complete post at http://wmug.co.uk/blogs/cliffs_blog/archive/2009/10/23/hyper-v-you-receive-windows-time-service-event-ids-24-29-and-38-on-a-virtualized-domain-controller-that-is-running-on-a-windows-server-2008-based-host-server-with-hyper-v.aspx