An Issue on Submitting Assignments and Tests with Essay Questions
We found the students who turned their Text Editor OFF are unable to submit assignments or tests that contain essay questions. The Text Editor tool can be toggled on and off in an Assignment and a Discussion Board forum, but there is No way to turn it on or off in a Test.
Advice: Before submitting Assignments or taking a Test with essay questions, be sure that the Text Editor is ON.
You can verify the setting in a few places:
Open an Assignment that has not been completed. If the Text Editor is OFF, toggle it ON.

Or
On the Welcome tab, select Personal Information from the Tools module. Click Change Personal Settings and make sure the Text Editor settings in Section one is On.
