Calibre da error al abrir, no carga nuevos libros ni permite envío al reader.

Da error al abrir calibre con este detalle:
Traceback (most recent call last):
File "site-packages\calibre\gui2\main.py", line 293, in initialize_db_stage2
File "site-packages\calibre\gui2\main.py", line 233, in start_gui
File "site-packages\calibre\gui2\ui.py", line 435, in initialize
File "site-packages\calibre\gui2\init.py", line 738, in save_layout_state
File "site-packages\calibre\gui2\library\views.py", line 546, in save_state
File "site-packages\calibre\gui2\library\views.py", line 540, in write_state
File "site-packages\calibre\db\cache.py", line 63, in call_func_with_lock
File "site-packages\calibre\db\cache.py", line 617, in set_pref
File "site-packages\calibre\db\backend.py", line 132, in set
File "site-packages\calibre\db\backend.py", line 128, in __setitem__
File "site-packages\calibre\db\backend.py", line 844, in execute
File "c:\t\t\apsw-9hooel\apsw-3.13.0-r1\src\cursor.c", line 236, in resetcursor
CantOpenError: CantOpenError: unable to open database file

Agradeceré si me alguien me puede orientar en la solución.