A couple of things you could do. Get an mp3 error checker and see if it has anything to say about the particular files. You also might want to grab EncSpot Pr

A couple of things you could do. Get an mp3 error checker and see if it has anything to say about the particular files. You also might want to grab EncSpot Pro (free, for windows) to figure out exactly what codec you used. Chances are that if the codec was buggy, then it's been documented such a google search on the specific codec and version will probably turn up people talking about the known errors.