From WikiTemp, the GBAtemp wiki

I have a gamecube disk image who's file extension is ISO, but it doesn't regard that as a GC-Iso in the open GC-Iso menu. I can't figure out what file extension it's expecting, so I don't know what I should rename my disk image to. No info in the crappy PDF file that comes with it either! This is the ABSOLUTELY WORST documented computer program I've EVER SEEN IN MY LIFE!!!!!