Wow this one blindsided me this evening.  I’ve just replaced the tiny 500gb drive in my main demo laptop with a shiny new 1TB one (I have a lot of VMs you know) and got hit with this error.  Basically what I did to replace the drive was use the free software from Acronis that came as a download with my new Western Digital drive to clone my 500gb drive onto my 1TB drive, standard stuff.  Having done that and trying to boot I got some lovely messages as as a result of doing boot to VHD and the the BCD no longer being able to find the files (because settings in the BCD had obviously changed)  to fix that I ran some simple commands:

diskpart

select vdisk e:\myvhd.vhd

attach vdisk

bcdboot <mounted vhd letter>\<vhdname.vhd>

And repeated for each of my bootable OSes.  All was good the OSes were working, but when I got into Windows Server 2008 R2 I couldn’t start any VMs….a quick look at the System Event Log revield the error

Hyper-v launch aborted due to auto-launch being disabled in the registry

And a quick Bing brought up this excellent article from SBSFaq.com so I needed some more commands to enable Hyper-V which doesn’t happen automagically.

bcdedit /set hypervisorlaunchtype auto

Finally I was done and my machine was back to normal.  Error fixed.