Just updated to the latest MOODLE_23_STABLE(20121101) and got the following error while upgrading the book module.

Notice: Trying to get property of non-object in /opt/veebid/vhosts/moodle.ut.ee/moodle/mod/book/db/upgradelib.php on line 117
Error writing to database

More information about this error

Debug info: Duplicate entry '70-2605' for key 'mdl_cont_conins_uix'
INSERT INTO mdl_context (contextlevel,instanceid,depth,path) VALUES(?,?,?,?)
[array (
0 => 70,
1 => '2605',
2 => 0,
3 => NULL,
)]
Error code: dmlwriteexception
Stack trace:
line 410 of /lib/dml/moodle_database.php: dml_write_exception thrown
line 1050 of /lib/dml/mysqli_native_moodle_database.php: call to moodle_database->query_end()
line 1092 of /lib/dml/mysqli_native_moodle_database.php: call to mysqli_native_moodle_database->insert_record_raw()
line 5138 of /lib/accesslib.php: call to mysqli_native_moodle_database->insert_record()
line 6646 of /lib/accesslib.php: call to context::insert_context_record()
line 117 of /mod/book/db/upgradelib.php: call to context_module::instance()
line 169 of /mod/book/db/upgrade.php: call to mod_book_migrate_all_areas()
line 627 of /lib/upgradelib.php: call to xmldb_book_upgrade()
line 358 of /lib/upgradelib.php: call to upgrade_plugins_modules()
line 1524 of /lib/upgradelib.php: call to upgrade_plugins()
line 329 of /admin/index.php: call to upgrade_noncore()

Any ideas? This upgrade surprised me, i hope the file references in my institutes moodle (around 1419) books and numerous book pages are still intact?