We are getting the error "A required privilege is not held by the client" while trying to execute any job on a Windows agent.
Secondly we are also getting an error while trying to restart the service manager service. As a result we had to manually start the agent.
Windows Server 2008 R2
Automation Engine 12.1.1
when you get this error message the WIN user that starts SMGR (or the WIN user in login object) does not have all the privileges that are needed - see agent installation documentation (chapter 3):