phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '-1' for key 'session_user_id'

INSERT INTO forum_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('a20c78c9aaee91157723d3d6f0fd42c2', -1, 1539870320, 1539870320, '36a6829d', -8, 0, 0)

Line : 187
File : sessions.php