http://en-americas-support.nintendo.com/app/answers/detail/a_id/2153/p/431
Above is a helpful link about disc issues. After going to the link, you will need to click the "Start Troubleshooting" button near the bottom of the page.
If the tips shown in the link above do not resovle the issue, please call 1-800-255-3700 to resolve the issue. If the troubleshooting does not come up properly, please reply back and I will put the information directly in a message. 