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 ('29bf1bcb87e0181c423aa6c689e9cfd7', -1, 1503323164, 1503323164, '369c3247', 5, 0, 0)

Line : 187
File : sessions.php