Sorry, we haven't had the time to dig through your source code. I've glanced at it and it looks like your problem is the splash screen. Don't put the AutomaticUpdater on your splash screen. Put it on your main app window. Or, if you have a pending update and you want to force it to be installed then call automaticUpdater.InstallNow().
Also, if you want to handle how the automaticupdater closes your app, then handle the CloseAppNow event and close your app from that event.