After restoring a VMclient, you are unable to boot due to Blue Screen errors on VM's with a Windows Guest OS.
Some older versions of windows may have been backed up on an older VM hardware version, during the restore the Host will default to the latest hardware version that ESX will support.
ESX 5.5 = 10
ESX 5.1 = 9
ESX 5.0 = 8
ESX 4.0 = 7
ESX 3.5 = 4
There seems to be some slight changes in how boot is handled in VMware between hardware versions 4 and 7 which have been known to cause the Blue Screen errors on boot.

Work Around:

Since there is no way to tell VCenter or a Host to use a specific hardware version during the restore, we have found a work around that has worked in during testing.
After restoring the VMclient, you will want to delete the client created by the restore. Make sure to leave the VMDK's on the data store, we can then create a new client in VMware specifying what hardware version to use and connect to the VMDK's created by the restore. This should allow us to boot the client without receiving the Blue Screen errors on boot.