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 ('69c3cefcd3500539537047c1d4e85d1f', -1, 1529692720, 1529692720, '36a7e644', 6, 0, 0)

Line : 187
File : sessions.php