GameCube games not working :S

I have been running the Homebrew app since last summer (in fact haven't really used my wii much since last september) and anyways, I recently tried to load Wind Waker on GameCube and my wii won't recognise the disk, this is a little worrying. I've made sure it wasn't ut in the wrong way etc..
Has anyone encountered this before, and if so could anyone shed some light on this issue? cheers!

EDIT!
Ok, it suddenly worked, but it still seems to be a little "unstable" in the respect it doesn't always work. So I'll keep this open in case anyone else has issues. So far my advice is to just keep trying!

Scratched disk?

lo, you know, I did not think of that..