Format Error?

I've recently found my mp3 player that has been lost for a while. I got it about 2 years ago i think. I tried putting on some new music to it last week. For some reason, I go to play the music on my mp3 and it just says 'Format Error' and won't play those songs. However, the last songs I put on it before it was lost went through without 'Format Error' coming up. Could someone please help me with this?

It is an AWA mp3 player, and I think the model is 512. (The sticker on the side says M512) The 2 cds which i tried putting music on from were Floorfillers Party Anthems 2009, and So Fresh Hits of Autumn 2005. The last cd I tried putting on before it got lost was Hilary Duff: Most Wanted. Please help if possible, thanks :)