[machine name] validation has failed. Machine [machine name] is paired to another Core. Protection is not allowed.

I rebuilt my Core machine and have added my vCenter back into the new Core. When I try to backup a VM I get the following error: "[machine name] validation has failed. Machine [machine name] is paired to another Core. Protection is not allowed."

How do I release the VM from the protection of the old Core? The old Core is no longer online or viable.