Colonel Howe, did you edit the music.txt? You should not do that. You need to convert simply your music files to .ogg, rename them with the original names (for example: wagner_ride_of_the_valkyries.ogg) and replace the old files.
Put in as many music files you whish, but not more than it contained in the original folder. If you have too less music files, doesn't matter. The music.txt will just detect this with the cant_find_this.ogg 0 0 line. For me it worked fine, I've done this before. But I think I can't upload this because of violating copy rights! :/