Try this:
Fettling methods:
1. Delete the directory you music is in. (Although it is a standard folder, so tread carefully) Then recreate it as an empty directory and fill it with music again.
2. Insert SD into a PC and do it that way.
Proper method:
1. You can delete the media files that you synchronized from your computer to your BlackBerry® device using the BlackBerry® Desktop
Software.
1. Connect your device to your computer.
2. In the BlackBerry Desktop Software, click Device > Device options.
3. Click the Media tab.
4. Click Delete all media > OK.
If all else fails
LINK.