I am not a mentor for that course and do not have access to it, but that type of message means that there is something fundamentally wrong with your notebook from a syntax perspective. E.g. did you download the notebook, work on it with some tools other than the course website and then re-upload it? E.g. running one of the course notebooks on Colab will overwrite the JSON metadata in a way that makes them unusable on the course website.
One easy experiment to try would be this:
- Kernel → Restart and Clear Output
- Save
- Submit to grader again
If that works, then it means that there was something in the generated output that confused the grader. The graders don’t need to see your output: they just call your functions with test inputs and check the results.
If that still doesn’t work, then one more thing to try, until we hear from a mentor who really knows this course, would be to get a clean copy of the notebook and then carefully “Copy/Paste” over just your completed code from the “YOUR CODE HERE” sections and then try submitting again. Here’s a thread about how to get a clean copy.