Is that the only location you have tried?
No, I’m not tried. The problem is in DefaultEditor.ini
I was worried it might have been the location character limit or that the folder was protected from being written to, both can be check if you try a different file location. I am guessing the other files were write correctly? If so, have you made other projects before with this version of the engine?
Most likely the issue is permissions. Try exiting UE4, then right click on the shortcut to launch UE4 and choose “Run as Administrator”.
If your Windows account does not have the administrator role set on it you will run into issues like this, you will need to either run as administrator each time or change your Windows account to an Administrator (if you own the PC that is, work/school won’t let you change it).