0x80042317 or Error: VSSControl: -2147212521

A task fails with the following error:

Failed to prepare guest for hot backup. Error: VSSControl: -2147212521 Backup job failed.
Discovery phase failed.
Cannot add volumes to the snapshot set.
Cannot add a volume to the snapshot set. Volume name: [\\?\Volume{c4e2fc39-0000-0000-0000-100000000000}\].
Cannot add volume to the set of volumes that should be shadowed.VSS error: VSS_E_MAXIMUM_NUMBER_OF_SNAPSHOTS_REACHED. Code:0x80042317  

0x80042317 translates to the VSS error “VSS_E_MAXIMUM_NUMBER_OF_SNAPSHOTS_REACHED”. This error is suggesting that there are too many shadow copies on the guest itself due to inability to delete or retention of existing shadows. This can also be caused by too many volume paths on the guest to be enumerated for backup. This limit is 64 volumes and is a limitation of VSS itself.
 
To check the shadows being retained by a system, open an elevated CMD prompt and run VSSADMIN LIST SHADOWS. This may take quite a while, depending on the amount of shadows enumerated. These shadows will either need moved or deleted.