Permission denied problem in notebook server (windows 10?)

We're having some problems with the notebook server and "permission denied" on windows 10 computer

Symptoms:

• Student starts up notebook server
• Student opens files in folder where they downloaded them
• Student adds their own code
• When they try to save, they are presented with a "Permission denied" error message

The result is that their solutions are on the screen in the web browser, but simply impossible to save.

I had this last week with two students

And today with one

And the problem is so bad on the one today that I could not, after trying multiple things, get his notebook server running again. (Often, if you restart the notebook server, you can just save as a new file. But this didn't work after me trying for 5 mins...)