Microsoft has published a KB article (KB2795043) that explains the following scenarios:
On System Center Virtual Machine Manager, you may experience one of the following symptoms:
- A Windows Server 2008 R2 SP1 Hyper-V host has a status of Needs Attention in the VMM Console.
- Adding a Hyper-V host or cluster fails.
The fix is … to uninstall the WMF 3.0 update (KB2506143). There’s a bit more to it than that. You also need to reboot the host and then run:
… and then do another reboot of the host.
I know; it’s far from an ideal situation. But there’s the workaround for you.