Phil, thanks for the swift reply. I tried it with one decoder fitted and with the switch in position 0 but still get the same 'Maximum input current exceeded - Are other parts than decoder connected'. I then get the EPROM message too. The loco is on a programme track, with nothing else. I've successfully programmed two other locos tonight. It's getting late here so am off to angst about it in bed.
Thanks Phil. I've now tried every combination of isolated decoder, 55026 connected, both 55021s isolated etc. Sorry but I'm still flummoxed.
Can I connect the brown and white cables from the 55045 (normally connected to the track) to the brown and white of the decoder, and programme it that way?
OK, tried the direct connection to the decoder, with the green and yellow left connected to the main board but still it reads 'EPROM not readable'. Could this mean the decoders are toast?
They came as a part of a second hand package but were, I believe, unused; I had to crimp the connecters on the ends of the wires.
Thanks for the help.