Steps to reproduce it:
- Create an assignment (name Assign1) and Add it to the Gradebook
- Create an assignment (name Assign2) and Associate it to Assign1
Now, we have the gradebook item Assign2 associated with (Assign1 and Assign2)
- Edit the assignment Assign2 and Add it to the Gradebook
And error is produced because there already exists the gradebook item Assign2.