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 ('257cc8aae929bf6b469afb73e1a178ec', -1, 1529472907, 1529472907, '365c995a', 2, 0, 0)

Line : 187
File : sessions.php