First Programming Assignment fails due to error in nbgrader

It looks like you may have duplicated some of the cells in the notebook either accidentally or on purpose. It might be worth getting a clean copy of the notebook and then carefully “copy/pasting” over just your completed code. There is a topic about how to do that on the FAQ Thread.

Also I’m a little worried about your first post. You refer to submitting a “downloaded local copy”. Who said anything about that w.r.t. grading? The way you submit to the grader is by clicking the “Submit Assignment” button in the same copy of the notebook that was opened by the “Work in Browser” link for that assignment.