In order for Diskshadow to take a VSS snapshot a Raw Device Map (RDM) is required. Once Step 5 has been completed navigate to the vCenter and perform a Rescan for storage.
Once the rescan has completed selected Edit Settings for the virtual machine and choose to Add a new RDM. When adding the new RDM you will see the VSS volumes.
Note:
The volume identifications will be different for each environment.
Connect each of the volumes as new RDMs and then connect to the virtual machine.