This error indicates that VSS has previously engaged with an attached Virtual Hard Drive (VHD) that is now not present, or a Virtual Machine (VM) is assigned to a VHD on a drive that no longer exists on the system.


Look in the VSS log (instructions here) for a line similar to that shown below:

Failed to locate D:\, skipping

Then reattach the previous VHD, or any VHD using the Windows Disk Management tool to the skipped drive letter (D: in the above example).