I recently added a bunch of music to my sd card for listening to while I'm driving. I've been using it for a few days, maybe 5 or 6 and it worked GREAT. Today, I was getting ready to go, and it said that 'music player cannot play this type of file.' although it's been playing it for a few days. In doubletwist, it said that the file no longer exists, when it definitely does. I deleted all of the music off and readded it. Now it works, but what caused that issue before?