Backup vCenter Server virtual machine with vSphere Data Protection 5.1

Hi all.

I'm using vSphere Data Protection 5.1 on a vCenter Server 5.1 infrastructure and I noticed that all bakcups works fine except for the vCenter Server virtual machine.

Looking at the logs, there are no errors, but the backup was not completed for this VM.

Can someone confirm that is not possibile to protect the vCenter Server Virtual Machine where the VDP appliance reside on?

Thanks