To-Do List Extra Assignments

When I look at the To-Do List on the Dashboard, there are several (16) assignments with the only content being: No course. When I click on one of them for details, I get no further details beyond it apparently being added by me, which I do not recall doing. When I try to delete it (after letting the delete button load), I get this error message: There was a problem deleting the assignment. Note that when I mark one as done, all 16 move to the Complete tab (and all go back when I click on one of the circular arrows). Any recommendations on how to actually remove these so that I can have accurate assignment numbers?