The restore fails because the restored files are not recognized as VM disks. When this restore failure occurs, it is because the VM that was backed up has disk files that are missing their .vmdk file extension.

At this time, it is unknown by Veeam Support why the .vmdk file extension could be missing from a production VM. If you experience this restore issue and the VM that was backed up is still present, you are advised to contact VMware Support to request assistance with investigating why the source VM is missing its file extensions.

The following is a workaround that Veeam Support has developed to allow for the restore of a VM that was backed up and had disks that were missing their .vmdk file extension.

1. Perform a VM Files Restore, placing the restored files in the destination datastore where needed.
2. Rename the -flat file to add the .vmdk extension.
3. Manually register the VM.
4. Check the VMs settings and confirm that it recognizes the disk files.

 

The current prevailing theory is that this may be related to an invalid template that was used to deploy the VM that was backed up, as often when this failure occurs for one VM, other VMs in the environment have been found to be missing their .vmdk file extensions.