Problem adding books to Kobo with Calibre

Hi.
Can anyone help. I have been using Calibre to add books to a Kobo eReader.
When I tried yesterday I received the following message. I tried 2 different books and received similar messages. Can anyone tell me what I need to resolve the problem.

Thanks

Error message I received in Calibre is below

Traceback (most recent call last):
File "site-packages\calibre\gui2\device.py", line 85, in run
File "site-packages\calibre\gui2\device.py", line 470, in _books
File "site-packages\calibre\devices\kobo\driver.py", line 1629, in books
DatabaseError: database disk image is malformed