phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '-1' for key 'session_user_id'

INSERT INTO phpbb_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in) VALUES ('5e1fa898c37e3efa5187b9f05a26e359', -1, 1419239231, 1419239231, '36ed97bc', 42, 0)

Line : 158
File : sessions.php