I have been trying to connect my laptop to an external monitor (different resolutions). My idea was to setup the external monitor as a clone of the laptop screen.

In Ubuntu Quantal's display settings I can detect both displays but I can only setup as an expanded dual monitor.

The mirror option is visible but disabled.

Is there a way to "enable" mirror mode?

Edit: In answer to ubunchu I'll try to be clearer. I merely want both displays to show the exact same image. I assume that the mirror option would do this but it is disabled.