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 ('2ef0a3a1c5e28e880991500e0b1d6e07', -1, 1467366806, 1467366806, '369ed119', 0, 0, 0)

Line : 201
File : sessions.php