Well, I've been a dev myself almost 30 yrs so I just began debugging......looks like it's simply a friggin disk io parsing exception......once I have many regbackups it occurs. Changing the target location via settings.ini to a temp folder with no existing reg backups results in the window now, instead of the ~30 friggin delay just opening before it even crashes (should have tipped me off), immediately opening and no errors.
Of note, a FRESH install is what first tipped me off because it ALWAYS opened once, and then also was fine after configuring with my options AND my existing target location, and in fact then allows a successful backup. However, clearly the app is periodically refreshing itself (for the purposes of preseting the existing backups in the "restore" tab I'm presuming), because my last testing showed that after a successful 1st backup to my existing location, if I simply let the window then sit totally IDLE and don't touch it, and in fact leave it on the very 1st backup tab.....after a couple of minutes suddenly out of nowhere, the very same user32.dll crash. Then of course, all bets are off because with the very well populated existing backup location now defined, the app will crash 100% and never even fully open for even a second until the existing backup location is removed.
Unfortunately, this is reproducible on ALL my systems (good handful) because as a good organized person I have pointed all of them to my central server's UNC (via mapped drive) to the same regbackup folder since this app automatically (and nicely IMO) creates a HOSTNAME subfolder in the regbackup target - but also means this bug once a regbackup target tree is large enough - will now crash not one but ALL the systems using this target storage.
I don't have the code obviously but let me know what (if anything) I can provide you for debugging. I love this app and have actually had to use the backups before so hopefully it is something you can hunt down in the code! TIA!