Attempt to run backup plan applied to a machine where Agent for VMware (Windows) installed causes this error:
Agent for VMware cannot back up the same virtual machine where this agent is installed. Use a different Agent for VMware to back up this machine.
This behavior is product design; agentless backup by using Agent for VMware (Windows) of a virtual machine where this agent is installed inside, is not supported. This error message has been implemented in version 8.0 to make you aware of this scenario and help to set up backups the best way.
Either use another instance of Agent for VMware to run agentless backup for affected machine.
Or install an Agent for Windows inside of VM and apply backup plan to this virtual machine only.