With Airtime 1.8.x, if you moved your stor folder, all entries in the database become invalid. What you need to do is run "airtime-clean-storage" and then re-import your files using airtime-import.
The good news is that we've fixed this problem in Airtime 1.9.0. File management should be much more intuitive, and no more of these hidden "gotchas" when moving your files around.