Problem:

Hyper-V VM guest (Windows Server 2003) on a Windows Server 2008 R2 host “randomly” loses network connection.

Symptom:

Unable to ping the VM from the host. On login to the VM error message “The system cannot log you on now because the domain <domainname> is not available.”

WLLogonScreen

Restarting the VM appears to solve the problem in the short term, but at some future time it re-occurs.

There are no useful messages in the Hyper-V log “Microsoft-Windows-Hyper-V-SynthNic-Admin.evtx or the VM Windows Server 2003 system/application event log.

Solution:

Host: Install the rollup package for the Hyper-V role in Windows Server 2008 R2 (KB2264080 http://support.microsoft.com/kb/2264080). Because the VM OS is Windows Server 2003, install the following updates:

http://support.microsoft.com/default.aspx?scid=kb;EN-US;981836

http://support.microsoft.com/default.aspx?scid=kb;en-US;2223005

Virtual Machine: Update the Integration Components in the VM 

See Also:
KB974909 :The network connection of a running Hyper-V virtual machine is lost under heavy outgoing network traffic on a Windows Server 2008 R2-based computer