Music Player can't see new mp3s all of a sudden

Hi, running 2.3.3 on a Galaxy S i9000. I have a whole batch of mp3s the media scanner won't pick up. I've tried copying them to my phone several times, rebooting, renaming the folder, moving files but it's like they are invisible to Music player/media scanner. However if I launch one of the mp3s from ES File Explorer, they launch fine in Music Player... Any suggestions?