Monitor Duplicating but Not Extending
 

I have four monitors set up and have recently installed the Targus Dock710.

I would like to extend to 4 displays.

I have downloaded the most recent driver from the DisplayLink website but for some reason my computer is only detecting 3 displays. It does however duplicate the 3rd display to my 4th monitor so there is nothing wrong with the cabling or connections.

I have clicked on each of the monitors in DisplayLink Manager and Windows display settings and ensured they are all set to extend. I have also tried detecting another display to no avail.

Can anyone help me extend from the 3rd monitor to the 4th.