Hyper-V Certificate Expiration and Resolution
If you are unable to open a Hyper-V mmc console and get the following message: "Cannot connect to the virtual machine because the authentication certificate is expired or invalid". Check out the following Microsoft KB http://support.microsoft.com/?kbid=967902
This applies to the following:
Windows Server 2008, Standard (Hyper-V role enabled)
Windows Server 2008, Enterprise (Hyper-V role enabled)
Windows Server 2008, Datacenter (Hyper-V role enabled)
Microsoft Hyper-V Server 2008
Patrick Lownds