The MP3音波 supports only MP3s (and limited to 128kbps or lower bit rate). Songs copy from iTune are likely not MP3s (could be AAC format). Try copy some MP3s and see whether it plays.
Can't do it that way... Well, if your have added a MP3 file into iTune then drag it out into your mini SD card, the file is still a MP3 file then it should be fine. On the other hand, if you converted a CD into iTune library and then drag this song into the mini SD card, it is an AAc file, and cannot be played...