Were they mp3 or m4a files? The extension & icon could be a telling factor. It 'might' also be they're encoded with a type that iTunes is not fully compatible with. iTunes cannot play all mp3 types out there. That's why I have a 2nd mac mp3 player that has xtra codecs. Tell us what the extension is. Oh & if the mp3 originated from a microsoft app then there's a reasonable chance you're right!