The custom keyboard shortcuts I set using the keyboard preferences windows is not working. 

As per [this](https://askubuntu.com/questions/297782/cant-change-keyboard-shortcuts-in-gnome-session-fallback-ubuntu-13-04-over-xdp) link I am able to assign custom shortcut for "show desktop" only. But my shortcuts for "File Manager" etc is not working.

How can I enable this?