Do you get that message every time you play? Does it happen with other games? I had a similar issue a while ago where my Wii was unable to read discs anymore and when I tried it would say something like "An error has occured. Please eject the disc and turn off the power and read the instruction manual for troubleshooting." and I ended up having to send the Wii in for repair. It seems like a somewhat common problem as I've seen many others experiencing the same kind of issue. Hopefully that isn't the case and you can just replace the game.