When you upgrade Process Engine server software, you must also upgrade the associated Process Engine Client files installed on other machines running FileNet® P8 components, for example, on Content Engine and Application Engine servers.
In a standard upgrade of your FileNet P8 system, you would install these client files in the course of upgrading each respective component.
However, if you are staging your FileNet P8 upgrade over a period of time and not upgrading one or more of the other FileNet P8 components at this time, you must still perform the Process Engine Client install on the other component machines.