Originally Posted by ghudod
I just had the exact same problem after updating calibre. It works fine again after reverting to 0.8.70. Looks like I won't be using version 9
Continuing to use a procedure ( NAS ) that has given you problems means you are running with a 'ticking time bomb' . NAS (and Clouds)are great for some things. A fast sequence of transactions (what Calibre does on a rename) is not one.
All you need is some other system change, to cause another failure.
This said. It is YOUR data