[josdb]

Originally Posted by kovidgoyal

That indicates your metadata.db is corrupted. The corruption is just not being encountered by older versions of calibre. You can fix it by following the instructions I gave in this thread:

https://www.mobileread.com/forums/sho...d.php?t=257215

I did that and everything seems to be restored, but I got the following message:

calibre, version 2.21.0
WAARSCHUWING: Gelukt: Herstel van de database is gelukt met enkele waarschuwingen. Klik Toon details voor meer informatie. De oude database is opgeslagen als: C:\Users\user\Documents\MEGA\Calibrebibliotheek\me tadata_pre_restore.db

Failed to restore the books in the following folders:
C:\Users\user\Documents\MEGA\Calibrebibliotheek\Sp ufford_ Francis\Red Plenty (74) with error:
Traceback (most recent call last):
File "site-packages\calibre\db\restore.py", line 253, in restore_books
File "site-packages\calibre\db\cache.py", line 57, in call_func_with_lock
File "site-packages\calibre\db\cache.py", line 1975, in restore_book
File "site-packages\calibre\db\cache.py", line 1483, in create_book_entry
File "site-packages\calibre\db\backend.py", line 804, in execute
File "c:\cygwin64\home\kovid\sw\build\apsw-3.8.2-r1\src\cursor.c", line 231, in resetcursor
ConstraintError: ConstraintError: UNIQUE constraint failed: books.id