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 ('f45e13a4279ed5cc5b84212b8b8e874a', -1, 1419122841, 1419122841, '3691f333', 5, 0, 0)

Line : 187
File : sessions.php