When selecting VSS via the Backup Options tab of the File-System Plugin, the option for 'Backup Through Mount Points' is greyed out.
While this may capable to do by giving the remote mounts Drive Letters, this is not a recommended practice by Microsoft, and Mounted Drives are typically excluded when VSS will be enabled on a volume. This is why this option is greyed out.
If it is necessary to backup through mount points, then use the 'Standard' Backup Method and select the option to 'Backup Through Mount Points'
