What was throwing me off was that the Accessibility selection is on the left. I kept looking at the top of the dialogue box. Duh!Here's how to get Snapper back working in Mac OS 10.9 (mavericks)
please open your System Preferences and then go to:
Security & Privacy > Privacy > Accessibility
Hit the lock
drag the Snapper application into the window (if it is not listed yet) and
make sure the check box is checked, like on the attached picture.
After you did this Snapper should work just fine.
Aram
Audio Ease