I have the exact same problem...stupidly I upgraded to 4.2j and can't play any non japanese games.
Should I try softmodding (looks bloody complicated)???
Don't use the DISC Channel, just use GeckoOS 1.93.
I have a Japanese Wii with D2CKey installed. I used anyregion_changer to convert it to a PAL Wii running 4.2E.
All my game backups work this way (all are NTSC/U or PAL). Notable exception is NSMB
I have a D2CKey in my Wii (NTSC) with Firmware 4.2 and I can only play games in my region. An update will available for this chip soon and can fix this problem, and can play NSMB. WiiKey2 update is available now.