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 ('46f387e3b4f58a9e31cf99c54abb86c1', -1, 1537651213, 1537651213, '36e0a68d', 6, 0, 0)

Line : 187
File : sessions.php