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 ('f8d037b067ec6c1a09807111acdb7e7d', -1, 1467366591, 1467366591, '369ed119', 0, 0, 0)

Line : 201
File : sessions.php