Week 2 Assignment Error - Platform Error: We're experiencing some technical difficulties

I can’t get grades in the 2nd week assignment called Practice Programming Assignment: Python Basics with Numpy.
FYI, it passed all the tests successfully.

It gives error as below:

Filename: nbgrader-part
0/100Score: 0 of 100
grading failed
Platform Error: We’re experiencing some technical difficulties
Please try submitting again in 10 minutes. If the problem persists for 24 hours, please reach out to Coursera through our Help Center.

In the screenshot you can see that there is one waiting in line. It happened after the “reset the kernel and outputs, then submit immediately” suggestion in this forum. The same strategy then resulted in the above error again.

I tried the new notebook solution, the manual write solution. It does not work. I don’t want to move on to the next one without getting the correct result. Thanks in advance and good work.

I was running on Ubuntu-Chrome on my dual boot system.
I switched to Windows and got my grade. That’s all I know, I don’t know why. Maybe it will give an idea to friends who have similar problem.
Good learning.

The Coursera servers were having problems earlier today. Probably a side effect of the AWS problems that were in the news.