In my case Repair and rest options did not help. Logging out and logging in to a personal account didn't help either. But strangely the following hack helped.
I was trying to create a notebook by the name of "Education". That caused an error. Please note I do not have and never had a notebook by that name in any of my accounts. But when I changed the name of the new notebook "Edication1" , it worked!
But then, there is no option to rename it! However there is an option to "nickname it" (Right click on the new notebook and select "Nickname Notebook"). So I used that and now the name of the notebook on the screen is what I wanted "Education", but the file
name remained "Education1". Its not ideal, but far less troubling than not being able to create a notebook.