Virtual Machine is unavailable and will be skipped from processing.  

This error occurs when a virtual machine's Managed Object Reference ID (MORef-ID) changes within the virtual infrastructure or the virtual machine is deleted. The virtual machine (VM) is still added to the Backup Job, and when the job starts, the job queries the vSphere infrastructure, attempting to find a VM with the MORef-ID that was recorded for that VM when it was first added to the job.

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 vCenter, may cause the VMs on that host to get new MoRef-IDs.
• Reinstallation or creating a new vCenter server where the old database is not reused will cause all objects managed by the vCenter to receive new unique identifiers.
  Customers are encouraged to utilize the vCenter's native file-based backup to protect and restore the configuration, ensuring unique reference IDs are preserved.

• The 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 VMs whose MORef-IDs changed now report as having the correct size.
  
• Please be aware that VMs 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.