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 ('3e434240e77ebfc17c9d6e208eb091b3', -1, 1540167288, 1540167288, '36e076f7', -4, 0, 0)

Line : 187
File : sessions.php