Power on VM failed; No connection could be made because the target machine actively refused it.

If you try to power on a virtual machine in vCenter Server 6.x and receive the following error “Error Received : A general System error occurred. No connection could be made because the target machine actively refused it.” then the most likely cause is that the “VMware vCenter workflow manager service” has not yet started. The service will by default start automatically and may be started manually if required.