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 ('ff9caa4bba0c2ac4ef1590aada4193b6', -1, 1467353391, 1467353391, '36519490', 41, 0, 0)

Line : 201
File : sessions.php