About the VSS_E_INSUFFICIENT_STORAGE snapshot error
During a snapshot, if VSS finds that no shadow storage area is configured for the requested drive it attempts to create a storage area. An attempt is made to create the shadow storage area on the same drive first. For example, if the D:\ drive is the requested drive, it attempts to create the shadow storage area on the D:\ drive. If it cannot create a shadow storage area on the requested drive, it tries to create a shadow storage area on some other drive.
If there is not enough room on the selected drive where the storage area is created, the snapshot fails with a VSS_E_INSUFFICIENT_STORAGE error.
Preconfigure a shadow storage area on a drive to avoid this issue. However, if that storage area is not large enough it can cause the snapshot to fail with the same error.
Another way to resolve this issue is to remove any stale snapshots that are present on the drive.
For more information about Microsoft's VSS, refer to the Microsoft website. You can use the error names as keywords when searching the Microsoft website.