The Wii is very picky with Media even some DVD-R will not work. What is recommended is DVD-R by Verbatim, Sony, TDK and some others, burn using ImgBurn at 4x speed for single layer games they currently all are except for SSBB. For SSBB use Verbatim DVD-R DL disc burn using ImgBurn at 2.4x speed.
The following thread has some more detailed explaination by Dark Mod.
You may also want to contribute to the following thread.