Hi,Over the last month I have been seeing errors on one NLB CA 2007node. The node did work well and event log was free from errors.The node seems to loose the network, it pings but is not availablethrough remote desktop. I have to gain access through the remoteaccess card on which the console locks - I then have to power off andon through the remote access card.When I reboot it seems fine and works for a time but then it stopsworking and repeats the same errors in the event log - errors arebelow:Event Type: ErrorEvent Source: MSExchange ADAccessEvent Category: TopologyEvent ID: 2142Date: 14/05/2009Time: 02:12:47User: N/AComputer: computernameDescription:Process IISIPMC03AD76C-E1F7-44C0-94C4-9C7F90AFA8F3 -AP"MSEXCHANGEOWAAPPPOOL (PID=1676). Topology discovery failed, error0x8007051f.For more information, see Help and Support Center athttp://go.microsoft.com/fwlink/events.asp.Event Type: ErrorEvent Source: MSExchange ADAccessEvent Category: GeneralEvent ID: 2501Date: 14/05/2009Time: 02:09:15User: N/AComputer: computernameDescription:Process MSEXCHANGEADTOPOLOGY (PID=1652). The site monitor API wasunable to verify the site name for this Exchange computer -Call=DsGetSiteNameW Error code=800703e5. Make sure that Exchangeserver is correctly registered on the DNS server.For more information, see Help and Support Center athttp://go.microsoft.com/fwlink/events.asp.Event Type: ErrorEvent Source: UserenvEvent Category: NoneEvent ID: 1110Date: 14/05/2009Time: 01:52:15User: NT AUTHORITY\SYSTEMComputer: computernameDescription:Attempt to determine whether user and machine accounts are in the sameforest failed (There are currently no logon servers available toservice the logon request. ).For more information, see Help and Support Center athttp://go.microsoft.com/fwlink/events.asp.A few weeks back we did experience a time skew, and the errors seem tohave occured since then.I have checked DNS and the records for the Exchange servers do exist.The server seems fine performance wise - not overworked but aswell asthe errors we have seen some virtual memory errors - the server doeshave plenty of memory and a suitable paging file.If anyone has experienced a similar issue then it would be good tohear from you.Regards,Julie

This issue is posted before. Check the solution;http://social.technet.microsoft.com/Forums/en-US/exchangesvrmonitoring/thread/2f0e7f45-5f4d-49c9-9a5a-ff53467dd355MCSE,CCNA,VCP,APP

It is purely networking issue, check your DNS settings and NIC setting, Update NIC drivers and run ExBPA to check if there anything which need your attention.Arun Kumar | MCSE - 2K3 + Messaging | ITIL-F V3