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 ('21be1d97d689a1b63a6d67d1b158f771', -1, 1513429166, 1513429166, '36e37e45', -1, 0, 0)

Line : 187
File : sessions.php