I have had a few files do this after playing fine a few times. It means there is something wrong with them or possibly they were made in some slightly dubious way. Some of mine also played ok in Real Player.
If you have a great number it is puzzling. I believe it is possible to repair mp3s I have not tried this but
See this link.
http://www.gnutellaforums.com/showth...126#post159126
You have nothing to loose .. give it a try and let us know how you get on