This doesn't sound very logical to me. Something that works a few times and then just stops until you reinstall, sounds very bizarre. We don't actually modify anything anywhere, or do anything that would even remotely explain it.
If it still happens with 24.0.75, can you post a log file of when its broken?
https://wiki.jriver.com/index.php/Logging
MC24.0.75 does not work at all. Here is what I did to create the log file:
1) Booted a working version of JRiver, MC24.0.41 and set the display to "Standard view" on Monitor #1.
2) Installed MC24.0.75
3) Boots properly into standard view on monitor #1. I eanbled logging to make a log file here.
4) select "Theater view" and monitor #2 displays the "Open GL Renders failed to load".
5) At that point the only choice seems to be to quite the program.
Again the video card is an Nvidia FX3800. I need this specific card because I output HDSDI (broadcast standard video) and not HDMI.
Where do I send the log file?
Thanks.