Last week, our iMac started behaving funny. Mail would crash every day. After some diagnostic checks, I learned that a memory module was giving an error. So, I replaced the large memory modules with the original 8 Gig that came with the iMac. Although the diagnostics were good with the replacement memory, Mail kept crashing. (New larger memory is on the way.)
So, off to the Genius Bar at the Apple store. Since this iMac is still under AppleCare, I wanted to be sure that this wasn't a hardware failure that might be expensive later. The previous iMac we owned before this one had a very similar problem that turned out to be something on the motherboard, not anything to do with software. Apple ran their tests overnight and found an operating system problem.
This computer had been running the most recent update of Sierra. Naturally, Apple wanted to install Mojave or Catalina. I chose Mojave.
After reinstalling everything from a Time Machine Backup, I tried to use the newest version of RUMLogNG to upload some QSOs to LoTW. I got the error messages that nobody wants to see.
After some interaction with Tom, we discovered a way to fix this. (I'll skip all the things that did NOT work.)
He suggested downloading a new copy of TQSL and installing it into the Application folder, but naming it something else. Then, in the RUMLogNG preferences, point to that "TQSL" application.
"Voila!" (That's a quite from Tom...)
That worked.
I then deleted the old TQSL, renamed the new one TQSL, and then updated RUMLogNG preferences to point to it. Still works fine.
If you're having sandbox issues, try this idea.
Thanks very much to Tom for his *very* patient help.