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 ('3c05aff232ba08b1f60745f97dafc13f', -1, 1406571988, 1406571988, '36c4a745', 41, 0, 0)

Line : 180
File : sessions.php