I can't add books anymore...

[OhIDont]

Ever since I downloaded the the 4th version of Calibre, it gives me error every time, "it's impossible to add the book"! So I tried downloading the 3rd version instead, and it's the same.
The error it gives me is:

calibre, version 3.48.0
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Impossibile aggiungere il libro:the WAR of ART - by Steven Pressfield [scanned book].pdf
C:\Users\picon\Downloads\Steven Pressfield - The War of Art_ Break Through the Blocks and Win Your Inner Creative Battles-Warner Books (2002).pdf
Con errore:
Traceback (most recent call last):
File "site-packages\calibre\gui2\add.py", line 414, in add_book
File "site-packages\calibre\db\legacy.py", line 225, in create_book_entry
File "site-packages\calibre\db\cache.py", line 62, in call_func_with_lock
File "site-packages\calibre\db\cache.py", line 1580, in create_book_entry
File "site-packages\calibre\db\backend.py", line 874, in execute
File "c:\t\t\apsw-mc0now\apsw-3.27.2-r1\src\cursor.c", line 236, in resetcursor
CantOpenError: CantOpenError: unable to open database file

[kovidgoyal]

Something on your computer, most likely an antivirus program is blocking calibre from accessing its database. Exclude the calibre library folder and calibre.exe from your antivirus and you should be fine.