It can happen that Accessibility permissions you have previously given an applet are lost. In such a case, you may see this message:
System Events got an error: 'Some Applet' is not allowed assistive access. (-1719).
Here's how to fix it.
1) Quit the applet
2) Open System Preferences > Security & Privacy > Privacy and click on Accessibility in the left sidebar.
3) Look for the name of the applet in the list. If it's checked, UN-check it, wait a moment* and then check it again. Launch the applet.
(*I cannot emphasize enough how important it is to WAIT. It may appear as though your clicks are not working. Just wait.)
4) If this does not work: quit the applet. Go back to Accessibility in System Preferences.
5) Use the minus button to remove the applet from the list.
6) Launch the applet. Eventually it will appear again in the Accessibility list. Make sure it gets check marked.
7) If this does not work: quit the applet. Delete the applet from the list as in 5) but this time drag the applet from the Finder into the list. Go to 6).
One of these methods will eventually work. It's a fragile thing for some reason.