Hi Ronnie,
Welcome to the site.
Can I get you to do a
FORMAT of your player please? Try within Windows first and then try playing your AMV videos. Of course backup what you want to keep before the format. Try that and let us know how it goes. It may have a memory hack on the player which is causing the "format errors" because you mentioned a video played before but now it won't which sounds very odd.
Take a look at this thread which is rather recent and similar:
http://mympx.org/forum/video-related/44020-solved-mp4-video-playing-problem.html#post281778.