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 ('1ae821acdb368e562cef897e4b1e0ae2', -1, 1416673146, 1416673146, '36a1dca0', 16, 0, 0)

Line : 191
File : sessions.php