After Upgrade to ESX 6.5 Update 2 DP 10.10 (Build 134) unable to backup vCenter appliance

We've recently upgraded a customer to ESX 6.5 U2 from ESX 5.5. The vCenter appliance is now running a UNIX client where previously it was Windows-based. We can no longer backup the appliance (this is a customer requirement) via VM backup - all other VMs are successfully being backed up. Also, when I go into the backup policy and select 'VMs and templates (original)' I get the attached screen error. Has anyone come across this?

VM Template Error.JPG