A snapshot from a previous backup has not been deleted (an orphaned snapshot). NetBackup should have deleted the snapshot when the backup completed.

Two policies try to back up the virtual machine at the same time. For one of the policies, the backup detects the snapshot that the other policy created.

Manually remove the orphaned snapshot.

For VMware, you can use the VMware vSphere interface to remove virtual machine snapshots. For Hyper-V, you can use nbhypervtool.exe to remove NetBackup snapshots that were created with the WMI backup method. For more information on nbhypervtool.exe, refer to the NetBackup Commands Reference Guide.

Reduce the likelihood of orphaned snapshots by changing the resource limits to reduce the load on the appropriate VMware or Hyper-V resource. The Resource Limit dialog is in the NetBackup Administration Console under Host Properties > Master Servers. The NetBackup guides for VMware and Hyper-V describe the available settings.

Change the NetBackup policy schedules to avoid simultaneous backups of the virtual machine.

For VMware only: Change the NetBackup policy's Existing snapshot handling parameter to a different option (such as Continue Backup).

For RHV only: Refer to the following article for steps to unlock the disk: https://access.redhat.com/solutions/396753. Then manually remove the older snapshots from the RHV manager.

For Nutanix AHV, refer to the Nutanix AHV Administrator's Guide to remove the VM snapshots.