Why won't my ps2 slim play my games?

I got a ps2 slim from my friend to play the ps2 game "Resident Evil: Code Veronica X," but every time I slip the disc in, it says that the disc cannot be read. I've tried some other games, like "Ratchet and Clank" and it works just fine. Are there some games that can't be played on the slim version, or is it just my disc?