The script checks the uploaded file mim type against the entry in "includes/upload_definitions.php". You can see the mime type in the error message:
MF27.mp3: Invalid file type (mp3, audio/mp)
Just add the mime type to the appropriate array in upload_definitions.php:
$mime_type_match['mp3'] = array("audio/mpeg", "audio/x-mpeg", "audio/mp3", "audio/mpg", "audio/mp");
If you add new file types you must ensure to add the extension to "Valid file extensions" in your settings. Note its a difference between mpg and mpeg.
Jan