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 ('991f1c6b002e42fe5949c06a5615b248', -1, 1555678187, 1555678187, '035b9dd5', 21, 0, 0)

Line : 187
File : sessions.php