You could try to replace the existing database with the one in the subsonic\db.backup folder.
1. Stop Subsonic service.
2. Move the existing content of subsonic\db to another folder. ( just to be sure)
3. Copy the content of subsonic\db.backup to subsonic\db
4. Start Subsonic service.
5. If all's well you can safely delete the files you moved in step 2.
if this doesn't help you could try the tip from
viewtopic.php?f=2&t=17878&p=75707&hilit=compact#p75707It doesn't seem to be relevant to your problem, but it might restore the integrity of your database.