Do you send the message to FARR's main window? How do you get that from DCUpdater?
i use some c++ classes that look up a Process ID given an application exe name, and then find the window corresponding to that Process ID.
there may be an inno setup addon that will do this, but it's not in default inno setup.
however, i can provide a smallish (50k or so) dll that you can call from inno setup that will find the process by name and send it the signal, and show how that can be used from inno setup if you like. i actually use this in all my installers to send a signal and actually CLOSE a running application during installation/uninstallation.