I'm still not sure what is triggering this, and what role the two different versions of FSUIPC are playing.
This error has been triggered by other issues as well (totally unrelated to FSUIPC), from my google searches. It may be some sort of timing change during initial load, with different programs or different versions of programs running, who knows.
I am going to have a good look at the RXP registry entries, and see if cleaning all those out and reinstalling it might also fix this. Kind of hard to link swapping in a different version of a different program (FSUIPC in this instance) as somehow affecting this lookup. We will probably never know the mechanism. What is clear, is that this is not a single one-off issue, as a number of folks have been affected.
The good side, is that all my RXP stuff is back now, and that anyone else that is similarly affected, are also likely to be able to get their setup fixed up as well.
* Orest