I think I've figured out what's been happening.
Out of the box all the new PA32DC OLEDs displayed Firmware version "B00T00" and at this stage they won't connect with ColourSpace.
I now believe that this indicates that a firmware upgrade has only been partially installed.
With one of the displays it was displaying "B00T00" but then after a few power cycles, started displaying "B00B06"
I know I didn't load this version, so it must have been loaded at the factory but not fully installed with multiple repowerings.
That's my theory and I'm sticking to it
Thanks for your help. Dave