Error communicating with device - no metadata table

Hi.
I'm new to the forum and hope someone can help. I've been using Calibre with Kindle on my iPad 2 quite happily for many months. But now I am getting an error when I connect:

calibre, version 2.48.0
ERROR: Error: Error communicating with device

no such table: metadata

Traceback (most recent call last):
File "site-packages\calibre\gui2\device.py", line 87, in run
File "site-packages\calibre\gui2\device.py", line 503, in _books
File "C:\Users\Tim\AppData\Local\Temp\calibre_vc11tj\2o 2uwc_ios_local_db\Kindle_overlays.py", line 113, in books
OperationalError: no such table: metadata

This is on a Win10 machine. But I decided to check OSX (El Capitan), so I installed Calibre from scratch and got the same "missing metadata table" when I connected my iPad to that. The Kindle app version is 4.16.

I'm stuck - so any assistance gratefully received!

TimK