Super Smash Bros. Brawl: Problem Reading Disc on Certain Characters?

About 2 years ago, my Brawl game was working perfectly fine. But after a year or so, Brawl would sometimes have a error reading the disc while I'm playing. I figured out its only on certain Characters that it can't read the disc on. Some characters work (EX: Meta Knight, Kirby, Samus) while others will have an error message saying that the Wii cannot read the disc when I try to play as them (EX: Mario, Link, Lucas). Anyone know what the problem is? My disc has very minimal scratches on it so I don't think that's the problem. Thanks for reading!