I discovered cause of the problem, all I had to do was set the attribute Archive in properties and NAND emulation to Partial for that game (as opposed to Full, which is the default in my setup). Now all games work on GX. It's really nice to leave my dependency on CFG behind at last.
Thanks for the help guys. And while we're at it, I've been meaning to thank you for giving us as such a handy app for some time,
Cyan. I love how it can be used not only as an USB game loader but also as an universal loader for nand channels, emunand channels, and apps. It took CFG ages to add support for most of these features (via unofficial updates), and even today, it still doesn't support all of them. Anyway, I've used GX as a system menu replacement for the last years and I've been really happy with it. So thank you
