After you restart the Hyper-V Host server and the guest virtual machines, you may encounter the error:
An error occurred while attempting to start the selected virtual machines(s).
Here are three common issues.
Issue 1
On a Windows Server 2008-based machine that has the Hyper-V role installed,or on a Microsoft Hyper-V Server 2008-based machine, you encounter the following:
• When you try to connect to a virtual machine, error occurs:
Cannot connect to the virtual machine because the authentication certificate is expired or invalid. Would you like to try connecting again,
• When you start a virtual machine, error occurs (Figure 1):
An error occurred while attempting to change the state of virtual machine ‘VMname’
'VMName' failed to initialize.
Could not initialize machine remoting system. Error: ‘Unspecified error’ (0x80004005).
Could not find a usable certificate. Error:‘Unspecified error’(0x80004005).
Figure 1: ‘Unspecified error’ (0x80004005).
Cause:
This issue may occur if the Hyper-V Virtual Machine Management service (VMMS) certificate has expired.
Solution:
Install the Hotfix.
You cannot connect to a virtual machine when the Windows Server 2008 Hyper-V VMMS certificate has expired
http://support.microsoft.com/kb/kb967902/en-us
Workaround:
Follow the steps below to generate a new certificate.
1. Shut down or save all virtual machines.
2. Restart the Hyper-V VMMS.
3. Start the virtual machines.
Note:As the Hyper-V VMMS certificate is valid for one year, the update has to be applied to prevent this issue from occurring in the future.