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 ('d1524a2ec81575dc20c59d37fc7e8e87', -1, 1467366647, 1467366647, '1714fc4b', 0, 0, 0)

Line : 201
File : sessions.php