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 ('61c6149ebec2035f11718f7fe1330bb1', -1, 1467353678, 1467353678, '36519490', 0, 0, 0)

Line : 201
File : sessions.php