While trying to use "Centralized Agent Upgrade" to upgrade an agent V11.2 to V12.1.1 an error message appear in the Messages window:
U00020965 Agent 'C105S188VM011_WIN': Upgrade to version '12.1.1+build.932' was skipped. Centralized agent upgrade not available for agents with version '11.2.3+build.401'.
The Centralized Agent Upgrade or CAU is a new features of v12 .
It cannot be used to upgrade v11.x agents.
Upgrade the agents from v11 to v12 manually.
Also the Service Manager has to be v12 for the CAU to work.