0x80042317 or Error: VSSControl: -2147212521

You receive errors on backup or replication processes during VSS guest processing.

0x80042317 translates to the VSS error “VSS_E_MAXIMUM_NUMBER_OF_SNAPSHOTS_REACHED”. This error is suggesting that there are too many shadows made 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.

Here is the error output directly from an Event Viewer occurrence of the issue:
 
The specified volume has already reached its maximum number of shadow copies. The volume has been added to the maximum number of shadow copy sets. The specified volume was not added to the shadow copy set. Other possible reasons: There is not enough free disk space on the drive where the locked file is located. Delete temporary files, empty recycle bin, etc. For WinXP, VSS has the limitation that only one shadow volume can be created per drive at a time. There could be another software that is already using the shadow volume for the drive. Restart your computer and try again.