Backup of the "X" VM has failed Source host could not create quiesced (application-aware) snapshot of this VM.
This problem happens when Windows cannot identify the recovery volume included in the Volume Shadow Copy Service (VSS) SnapshotSet during the VSS process. The reasons are the following:
For more information, refer to the VMware article.
To solve this problem, use BIOS boot and utilize the MBR disk layout or fall back to the filesystem-consistent snapshot.