意外的文件结束意味着远程服务器接受并关闭了连接而不发送响应。远程系统可能太忙而无法处理请求，或者存在随机丢弃连接的网络错误。

"Unexpected end of file" implies that the remote server accepted and closed the connection without sending a response. It's possible that the remote system is too busy to handle the request, or that there's a network bug that randomly drops connections.

根据可用信息，无法说明发生了什么错误。如果您可以访问相关服务器，则可以使用数据包嗅探工具查找确切的发送和接收内容，并查看服务器进程的日志以查看是否有任何错误消息。

With the information available it's impossible to say what's going wrong. If you have access to the servers in question you can use packet sniffing tools to find what exactly is sent and received, and look at logs to of the server process to see if there are any error messages.