I have just discovered that I can't add any instance of any activity module anymore. I'm not sure when my moodle installation got that way, or what I could have changed to make it happen!
Whenever I try to add an activity to a course, I get an error message on the confirmation page that reads:
"Could not add a new instance of _______"
Whatever activity I was trying to add has it's name in the blank.
This may be tied to another problem I'm having with the Forum module, with forum icons multiplying on their own on my course pages......