In the "Main menu" block, the action to move left is throwing an exception. 

Steps to reproduce:

1. Log in as administrator
2. Go to the "Home" page
3. Add "Main menu" block
4. Add a new activity and return
5. Click on "Move right" in the action menu for the activity
6. Click on "Move left" in the action menu for the activity
   1. Exception will appear

Extra notes:

This is likely happening because course/mod.php is expecting indent="-1" parameter to move left, and the action link is adding indent="0" parameter instead.