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, session_admin) VALUES ('ac97a93a313a2e53e93c2f2d0891bbc7', -1, 1406696301, 1406696301, '3657864a', 54, 0, 0)

Line : 180
File : sessions.php