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 ('535fd129bae7cd3e6e7df871b747d47a', -1, 1540067642, 1540067642, '36a16418', 8, 0, 0)

Line : 187
File : sessions.php