Arg, yeah... the import music is quite sensitive... (Maybe your song's names have spaces or special characters?)
I would suggest you to check the Music section of the forum, some interesting posts about limitations of the music for NESMakers, what you can't do, what you need to check...
And this post: http://nesmakers.com/viewtopic.php?p=8897#p8897 and http://nesmakers.com/viewtopic.php?f=4&t=219