In case if you’re testing Windows 2012 VM’s on Windows 2008 R2 HYPER-V host then you better apply hotfix 2526776 to the host computer. If you miss the update you’ll experience following symptoms in your Windows 2012 VM’s
- The Windows 8 or Windows Server 2012 virtual machine stops responding.
- The Windows Server 2008 R2 host computer displays a stop error message and restarts automatically. This behavior brings down all other running virtual machines together with the host computer
Applying this hotfix will require restart on your host computer. But I d hope at this stage most of you have already moved your test lab servers into Windows 2012