Virtual Machine is unavailable and will be skipped from processing.  

This error occurs when a virtual machine's unique inventory reference identification number (MoRef or Managed Object Reference) changes within the virtual infrastructure, or the virtual machine is deleted. The virtual machine is still in the Backup Job, and when the job starts, the job is still attempting to find the VM by its old reference ID.

Note: The most common events that cause a VM MoRef ID to change are:

• A VM is removed from inventory and then added back to inventory.
  
• In rare cases, a host crash, which prompts the host to be removed and added back to the VC, may cause the VMs on that host to get new MoRef-IDs.
• Reinstallation or creation of a new vCenter server where the old VC database is not reused. (If this occurs and all VM's MoRef IDs have changed, it may be possible to resolve this en masse using the vCenter Migration tool here: https://vee.am/kb2136)

• Resolution can be confirmed without running the job. Edit the job, navigate to the "Virtual Machines" tab, and click the [Recalculate] button. Note that the VM's whose MoRefs changed now report as having the correct size.
  
• Please be aware that VM's are tracked by their unique MoRef ID. When the MoRef changes, the VM is considered an entirely different VM. As such, Veeam Backup & Replication will treat them accordingly and create a Full restore point for the "new" VM.