the programmer software had a bug in it, whereby it would not copy the existing bandgap (calibration) bits.
This caused my devices to be rendered useless as there are too many variables to the factory set defaults, so i can do one of 2 things:
Send the devices back to microchip for re-calibration;
or
Chuck them out and buy a cupple more.
I have chosen the latter. It appears that these bits are factory set and once this data has been lost, it cannot be recovered!