I never can read the error message on my screen when I load the backup launcher and it fails...but there have been two reasons I have gotten error messages in the past:
1. Incorrect installation of IOS and CIOS - if the wrong CIOS is installed, or the DVDlib isnt installed, then the backup launcher won't have access to the disc drive. Go to
http://www.wii4everybody.com/2008/11/wii-b...r-03-gamma.html for the step by step instruction, it worked for me.
2. Iso is incorrect or the DVD media you are using is not compatible with the Wii. I spent several hours trying different isos and burning methods and DVD+R's and DVD+RW's trying to figure the best combination that will work. I found that for my burner and wii, Maxell DVD+RW's burned at 4x through ImgBurn (a free app for burning iso's) worked best, but your situation could be different. Most 1:1 isos will work, but a few need to be patched or BrickBlocker 'ed. It shouldn't be too hard to google these tools.
I hope this helps, because I understand how frustrating this is. Two days ago I stayed up until 8 in the morning working on it, and I finally got things working last night. So far I have managed to get GHWT, Mario Galaxy, Metroid Prime 3, Excite Truck, and Castlevania Judgment running, and so far none have failed under the circumstances I have described in #2.