Generally you get this error whenever remote server sends you a RST packet, which indicates an immediate dropping of the connection, rather than the usual handshake.
There could be many issue for this error from server side and only server administrator can troubleshoot and fix the issue. If it is temporary issue, you can reload your page in the browser.
For server administrator, if this error appears for all users, there should be some issue on the server which requires further investigation. It is also possible that website owner has restricted the access to server and or website and he is sending RST packet for unknown request.