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 ('6e2f088b264a709b174803fb233fadde', -1, 1513239216, 1513239216, '365bab89', 6, 0, 0)

Line : 192
File : sessions.php