Hi Tuftedduck!
Having done my daily ablutions and Sunday oblations, I had another go with the printer powered off and the usb pulled from the printer, still with no luck.
I'm now getting slightly confused, as the dialog box says printer and computer should be connected. Have I read you incorrectly, may be that the total sequence of my efforts is wrong; that the addon has to be first in the sequence of installs before anything else?