I am facing the same issue...even a simple alert script is not getting triggered
On ML 10.8.1, I have created a new empty folder called Actions, and through the services menu item, selected Folder Actions setup ...
Then, I chose "add - new item alert.scpt," and then enabled each check box just as you have done.
I did not choose to edit the alert.scpt item.
When I drag and drop a new file (in this case, a PDF file) into this folder, I get the expected functional alert pop-up: