This error means that the data port between you and the server to which you are trying to connect is not open (blocked or closed by your Router or Firewall) If you are using the Active mode of connection then open ports 20 and 21 in your router or firewall. If you are using the Passive mode of connection then open ports 21 and all ports above 1024. If you are still not able to connect then check all devices, like routers, between your computer and the server to see if the specified ports are open.