I had the same problem, running Xubuntu 14.04 on a AO-D255. every time I'd push the Fn key and left or right arrows to control brightness for every time I'd hit the button the 'Display settings' window would appear. Finally I was able to find this solution and seems to be working fine. I take no credit whatsoever. it worked for me, hopefully for you too.
Move the original file (in case you decide to revert the changes; yes, it is the
sudo mv /usr/bin/xfce4-display-settings /usr/bin/xfce4-display-settings.original
Create a fake file:
sudo cp /bin/true /usr/bin/xfce4-display-settings
xfce4-display-settings (native code) just returns
true to keep the calling application happy. (I don't know which daemon keeps calling it).
- Logoff/logon; Enjoy XFCE4. Of course your "Display" in xfce settings won't work now, so you'll want to install 'lxrandr' via Software Center to get the functionality. It's icon will be the same but called "Monitor Settings"
You may have to repeat this after distribution upgrade."