MediaPlayer10 Stops playing purchased media

I recently upgraded to V. 10, and 1 week affter doing so, all my purchased music will no longer play. I get an “Unknown error” that tells me it will not play copyrighted media. It now will also not burn anything. I contacted Wal-mart.com (where I bought my music) and they tried to help. So I have a lot of money in music, but cant play it. This has to be an error with MP10. I am not a big techie, just do the work for a local courier company of 5.