Are you in Composer and is a job open in Composer when you enter Shift +F11? If you are then the next thing that should happen is that a second program named GSPPlot should open containing the job you just outputted from Composer. You will then use GSPPlot enter print and plot parameters and to send the job to your Edge and later to your plotter.
If the first half is correct then check in the Gerber Program Group to see if GSPPlot is actually installed. If the first half is not correct, then do it as described.