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 ('91ea39f64f021259e808f7cde643df0d', -1, 1534602218, 1534602218, '36c660c6', -7, 0, 0)

Line : 172
File : sessions.php