I just uninstalled FMS 15 without any problem. After reboot, I tried to install FMS 16 but I got this message saying, 'Apache server is running, stop it before running this installation program (translated from French).
I have tried to stop the service : sudo apachectl stop
but I'm getting this error : /System/Library/LaunchDaemons/org.apache.httpd.plist: Could not find specified service
macOS Sierra 10.12.4