Adding ESXi VMs to agentless protection either new protected or previously protected fails with:
Quest does not provide support for problems that arise from improper modification of the registry. The Windows registry contains information critical to your computer and applications. Make sure you back up the registry before modifying it. For more information on the Windows Registry Editor and how to back up and restore it, refer to Microsoft Article ID 256986 “Description of the Microsoft Windows registry” at Microsoft Support.
Perform these changes in the core's Windows registry to fix this issue:
Retry adding the VMs to agentless protection.