Windows 8 and importing VirtualBox VM's into Hyper-V

Upgraded to Windows 8 this weekend and it's definitely nice and painless. Other than the new start menu and the loss of Aero it's really not much different to Windows 7 externally, and after the upgrade all my apps continued to work like before as if nothing had changed.

The only real issue I had initially was with VirtualBox. The version I was running won't run on Windows 8 (the latest might do), but that wasn't an issue as I was already planning to switch to using Hyper-V instead. Importing my existing .vhd's into Hyper-V should have been straight forward, but I kept getting errors similar to this :

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New Virtual Machine Wizard
The Virtual machine management service encountered an error while configuring the hard disk on virtual machine <Guest name>.

Failed to add device 'Synthetic Disk Drive'

'<Guest name>' failed to added device 'Synthetic Disk Drive'. (Virtual machine ID xxx)

 

The Virtual Machines configuration xxx at '<Hyper-V Path>' is no longer accessible: The requested operation cannot be performed on a file with a user-mapped section open (0x800704C8)

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when I tried to create a new VM using the existing vhd as the disk. The issue turned out to be AVG and its resident shield scanning the files as mentioned here http://support.microsoft.com/kb/961804, once I'd excluded all those folders I was good to go and things started working.