Have you had any luck resolving this issue yet? I'm having the exact same problem as you are...
I've got a NTSC/U Wii, 3.1U with a Wiikey 1.9s. I use Verbatim DVD-R DataLifePlus media, I burn with Nero at 4x, and this is the same process that I have used for every other Wii game I have (200+)...