The underlying connection was closed: The connection was closed unexpectedly.

基础连接已经关闭: 连接被意外关闭。

基础连接已经关闭: 发送时发生错误 

The underlying connection was closed: 在一个非套接字上尝试了一个操作。

防火墙问题。或是杀毒软件，卫士之类的。(360 卸载 )