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 ('6a584f3057ac559cb85394029b0ee6f4', -1, 1435814079, 1435814079, '365063e8', 5, 0, 0)

Line : 189
File : sessions.php