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, is_robot, session_admin) VALUES ('9932cd802a62dc03586e7b44307b8c03', -1, 1454987548, 1454987548, '1716e716', 8, 0, '0', 0)

Line : 174
File : sessions.php