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 ('6538f8c6bb71a392812f98ed3df4f8b0', -1, 1539941426, 1539941426, '369c27f5', -4, 0, 0)

Line : 187
File : sessions.php