Hi everyone,
Well I had the exact same problem until today. I was burning discs at high speed like 16x or 8x min. At first it was ok but it started to give a lot of DRE messages lately, it even could not recognize some discs at all.
Today I tried to burn the same games with 4x and all of them worked like a charm. No DRE, no not-recognizing the disc. It's perfect.
If you burned them at high speed, try 4x.
Edit: Sorry I forgot to tell, I have NTSC, Wiikey installed Wii with the latest updates installed.