I have an existing node of the book content type. This node was migrated from Drupal 5.x to Drupal 7.14. I noticed the page was not assigned to a book so I tried to create a book with this page at the top level.
I got a message that an unexpected error had occurred and that I should try again later. I checked the watchdog and found this message: PDOException: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '3' for key 'nid': INSERT INTO {book} (nid, mlid, bid) VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2); Array ( [:db_insert_placeholder_0] => 3 [:db_insert_placeholder_1] => 1598 [:db_insert_placeholder_2] => 3 ) in _book_update_outline() (line 652 of /dnc/democratsabroad/v3.1.44-staging/drupal/modules/book/book.module).