Do you have a disc-cleaner? This is a typical dust problem, I had a similar one for me on Age of Mythology (I think). I couldn't see the names of the ones I wanted to challenge. I washed it and it was OK.
If you don't have a disc-cleaner, use a glass-clean-handle or something.
http://www.vgchartz.com/games/userreviewdisp.php?id=261
That is VGChartz LONGEST review. And it's NOT Cute Kitten DS







