According to this, a small but significant number of Super Smash Bros. Brawl purchases are showing disc errors in the US, but Nintendo has moved lightning-strike Pikachu stylt to make everything good.
“Super Smash Bros. Brawl utilizes a double-layer disc which has a large memory capacity,” said Nintendo. “A very small percentage of Wii consoles may have trouble consistently reading data off this large capacity disc if there is some contamination on the lens of the disc drive. Nintendo has specialized cleaning equipment that can resolve this problem.”
If you’re American and having issues, hit that link for a form to fill in and Nintendo will clean your laser for you. There’s service.