The "weird jpg" was just a screen stip I took of the error message which I had inclluded in my email to Adam.
I initially found the problem appeared to be a fault in a "custom turnout" I had setup
a number of years ago - a return loop with a couple of points included.
When I edited the parameters file to remove it - the original problem disappeared
But then I found I still had problems when saving in Version 5-2-0 GA
and then getting errors when reloading the file, with only part of the layout being displayed.
After a lot of to & froing between 5-2-0 & 5-1-2a
- Removing various layers & individual items:
a) Load original in 5-1 - remove layers/items & save with new name.
When I remove the four of these I had in two layers, then the new version now works