You can follow my tutorial posted, you can start at the step that says cIOS Downgrader. This requires a good internet connection and this will help you downgrade to firmware 3.2 in which case starfall is a good idea to install as well.
This is NOT required to solve your problem.. The error you are receiving is related to the media you are using.. Either you are using DVD +R which this error occurs most often for, or your wii just really doesnt like your media.
Try one of the following:
Try burning in ImgBurn. If you DO have DVD+R make sure it is booktyped to DVD-ROM
If your media is DVD-R dont worry about the Booktyping. But make sure that you dont have a lot of other programs running in the background while you do your burn. This means close internet explorer, possibly turn off your antivirus temporarily, whatever it takes.
If neither of those works, pick up some DVD -R media with a different brand. Verbatim seems popular but I think in general just pick up any other brand to try with and go from there. If those dont work, return them and try again
I use memorex, so it really doesnt have to be a 'brand' name