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 ('d7d0f5bea0c5881340e1afd642a2ea0f', -1, 1540160458, 1540160458, '3691534f', 9, 0, 0)

Line : 187
File : sessions.php