Huh. I typed out a long reply, hit send, but it just disappeared. The partition is FAT32 formatted, with 32KB clusters, verified in Acronis Disk Director 11 Advanced.
I haven't tried other loaders; someone suggested WiiFlow to me and I may give that a shot.
candy - I did follow all of the steps you mentioned (installing DIOS MIOS via WAD Manager using cIOS 236). I'm going to give your suggested options a try. Do you know if I can rip a GC ISO using a computer, instead of my Wii? I have the game, but my Wii's disc drive is bad.
Also, as a side note, I really appreciate the help you have both offered. Thank you both. :)
Since you have a low post count and had http links in your post, our system auto moderated your previous post. It is now viewable...
If your Wii games works with your USB Loader then the GC games may work also, do you get a DIOS MIOS splash screen, if not then it maybe your USB HDD is not supported try another USB HDD or flash drive.
With DM 2.6 you do not lose the ability to play retail GC games, just load it from USB Loader first then the disc channel, all my retail GC disc works perfect from disc channel with DM 2.6 install. Use your friend Wii to rip your GC games with CleanRip or any USB Loaders or if you own the games maybe you could get a digital copy, use DMToolbox to convert it to correct format, select RAW and Align: 32k and you could also try wiiflow v4.0.5 or dios-mios-booter r30 You may have to try a few different GC games to know if DIOS MIOS is working, the DIOS MIOS splash screen is important.
I install DIOS MIOS 2.6 for USB because I have a lot of GC games but you could install DIOS MIOS Lite 2.6 for SD and put the GC game in your games folder on your SD and see if it work, if it works from SD then the GC iso is good and it may just be your USB HDD is not supported.
DIOS MIOS has to detect the disc drive for it to work but you do not need a disc in the drive.