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 ('49c10af8b6e619a4fab4f006e2eb7ca0', -1, 1540062516, 1540062516, '36a16418', 6, 0, 0)

Line : 187
File : sessions.php