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 ('121b9918ad587c8a49eb0d4e1d55edff', -1, 1529893956, 1529893956, '365c995a', 41, 0, 0)

Line : 187
File : sessions.php