While there can be multiple reasons, I remember that I faced similar issue because I had opened the same notebook on a desktop and on a laptop, and while the session on the desktop was still active, I tried to update the session through the laptop. There was previously also issue of Kernel dying for some reason, so please try to restart the kernel, by going to Kernel option in the top menu.
I tried all the options around restarting, restarting the coursera, restarting the kernel and restarting the laptop itself, still getting the same error.