Why aren't any of my Folder Actions triggering?

I'm running Mountain Lion (10.8.3). I have three or four folder actions set up which stopped working some time ago, and I can't figure out why. Thinking it could be a problem with the scripts, I created a new folder named "Test" on my desktop, and attached the "add - new item alert.scpt" sample script. When I created a new text file in the folder, nothing happened. I checked the system log to see if there were any error messages being output, but I couldn't find any. (In fact, searching the system log using Console.app for "folder" didn't produce any results at all) How do I figure out why none of my folder actions are working?