It seems there are quite a few people who are having disc reading trouble for Xenoblade Chronicles. Well, Nintendo Support has a page for you that better describes why it might happen and what you can do about it.
Nintendo Support 

Ryan Tyner
Ryan is an owner and manager of the oprainfall website, mostly managing changes needed for the website and maintenance. He also writes articles from time-to-time. His gaming interests include mostly RPGs; both Western and Japanese. Ryan has a graduate degree in psychology.