phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '-1' for key 'session_user_id'

INSERT INTO forum_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('dac8a0b4c547333975dd26a7a8e83b76', -1, 1540341470, 1540341470, '36a16418', 15, 0, 0)

Line : 187
File : sessions.php