Curtis MP3 player help?

I have a Curtis Mp3 player. I have had this player for over two years. For the most part,it has worked fine with no problems,but I have noticed that the player skips playback in some songs (similarly to how a CD player skips playback in defective CDs.) Sometimes it will play a song for roughly a minute or so,then stops playback,and the message "Format Error" appears on the display. Then the player skips onward,by itself to the next song. (Note: This only happens in some songs but not others,I know it's not a copyright issue,because it only suddenly started to do this with some songs,songs which used to play perfectly on that same player at one stage,)but that is not the case now). This happens with some select songs only,and its always the same songs this occurs with. What could be the problem? Thank you.