Ok so you have decided to upgrade your Virtual Server installation to the latest version SP1. So you want to minimize the downtime and save the states of your running virtual machines and you do the upgrade (stopping the services like it warns you) and when you attempt to resume your virtual machines you get a weird error like
<Virtual machine name> could not be restored because of a host processor type mismatch or hardware assisted virtualization is required, but not available.
You scratch your head and possibly say a few words I cannot repeat here, or maybe in reverse order ;-)
You did not change any hardware all you did was upgrade to the latest service pack, what is going on.
So here is what you did wrong (ok not all your fault)
You did not read the release notes very carefully, well actually you might have, but there is a slight problem with them. There is a highlighted IMPORTANT note under Installation notes that says
You must shutdown all guest operating systems or turn off virtual machines before performing the installation, including any virtual machines that are currently in saved state. This is important because saved states are not compatible between Virtual Server 2005 R2 and all previous versions of Virtual Server 2005.
The one issue is that the last sentence in the note should read
This is important because saved states are not compatible between Virtual Server 2005 R2 SP1 and all previous versions of Virtual Server 2005.
So you now know that you must power down all virtual machines before you upgrade because the saved states are incompatible.
So what do you do now, your options are:
1) Uninstall SP1, reboot and reinstall R2 version, then resume all VMs in saved state and power them down. Once you are done doing that then you can upgrade to SP1 again.
2) Discard the saved states of the machines that will not boot and then they will start. (this is like pulling the plug on the running machine and you will lose any data in memory)
Option 1 can take some time if you have many VMs, but will not result in data loss. Option 2 is very fast, but you could lose something important.....you decide.
Hope this helps you out of a spot.