There are environments with many Policy Servers being administered by few AdminUI's.
If an upgrade from CR2 to CR5 is required, this needs to be planned properly to avoid running into potential compatibility issues.
As such following questions came up:
AdminUI should be at the SAME SP and CR level as policy server it is administrating.
If the adminui is at a lower sp/cr version, upgrade the adminui to use the same version as the policy server.
If the adminui is at a higher sp/cr version, please remove the old adminui version and install the same version as the policy server unless you plan on upgrading the policy server to match adminui version already installed.