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 ('0f964eb6077b0aa259e254e2be600176', -1, 1416986979, 1416986979, '3652d198', 16, 0, 0)

Line : 191
File : sessions.php