This appears to be a 'factory reset' that takes the MX-850 back to standard settings. I did this and then re-downloaded my own MXF file. Unfortunately, the problems still remain. By the way, where is this reset facility documented?

To answer your other question, I'm not using any USB to serial adapter.

I have a POWER device page that carries all my discrete power on/off commands. They all used to work and, with one exception, they all still work when tested via the MX-850 Editor. The exception is the DVD, which now needs two DVDON signals to turn on and two DVDOF signals to turn off. However, only one of these power commands work when issued via the MX-850 (and that is the only macro, the rest are all simply learned IR codes). Does this behaviour give anyone a clue as to what might be going wrong?

I've tried relearning some of these codes but it made no difference (and indeed I wasn't really expecting a difference since the codes were already working via the editor). In every other respect, my MX-850 seems to be working okay.