So, after an unforgivably long absence, I'm back again. And as I mentioned in my direct reply to you, Skwire, I did note that there was an updated version of MPCPLEditor which I now downloaded and tried out.
Sadly, things when from good to bad. Of course, I still have the old EXE that I can run and open MPCPL files just fine. However, with this new version (dated 04/05/2018), it won't open the MPCPL files. When I choose FILE -> OPEN, and then select the appropriate MPCPL file, the app briefly loses focus and then… nothing. Granted, I'm not any kind of a programmer, so I'm at a loss as to what's wrong. I thought originally that it might be because I've had my computer running continuously for the last week, and even though I've got lots and lots of RAM, HD space, and low CPU usage, I figured: What the heck, reboot the PC.
So I did that and tried the new MPCPLEd.exe. Same problem. The next step I tried was to temporarily disable ALL programs that start up on my PC automatically, no matter how unlikely it is and then reboot and try again.
So I did that, too, and when I open MPCPLEd.exe now, it *still* doesn't work. I guess I'll need to put the ball back in your court, Skwire. Please let me know how things go, and I'll keep in touch for the next week or so. I hope I can figure out what's not working.
If it helps, my system info is listed below my signature. And as I mentioned in the previous tests mentioned above, I rebooted with all off except for my Anti-Virus (Avast Premier). Also, with regards to the MPCPLEd.exe program I'm using, the HELP -> ABOUT screen shows the exact same for both versions. The only diff I can see is that on the older version, my screen handle is misspelled which helps me tell them apart because the are both the same "v1.0.1 build 1" and the two executables are slightly different sizes.