Will Johnston wrote:
Problem solved offline with assistance from vBackup support team. The VM contains a "#" in its name which also appears in the storage folder. However the https connection vBackup uses to access the datastore does not encode the URL to take account of special characters.
Problem resolved by unregistering the VM, renaming the storage folder AND VMX file and finally re-registering the VM in vSphere.

Thanks, resolved an issue for me. Beside rename VM, I had to rename Datastore, there was a "+" sign in the name