I’ve seen the notebook and it turns out that the whole beginning section has just been deleted. Here’s what it looks like:
Why did you do that? It’s a mistake in general to modify things outside the “YOUR CODE HERE” segments. It’s not illegal, but you need to be careful when you do that. You must have trashed some of the JSON metadata that is not visible in the notebook, but which the grader depends on.
Please get a fresh copy and then copy over just your code from the “YOUR CODE HERE” segments and then try submitting to the grader again.
Please let us know if that resolves the problem for you.