" If one goes to the Homework Sets Editor and presses SAVE once, the error mechanism is in some sense turned on, but the error itself does not happen. THEN clicking on any of a lot of things will trigger the error, such as clicking on Student Progress on the left side bar. One gets the same error message.
The reason I found that noteworthy is that clicking Student Progress reads data but does not save data, so far as I know. So whatever happens is associated with a file action, but it is not necessarily a save action."