C＃UDP套接字无法接收消息

I'm having problema to receive message from UDP socket. I have made C++ server and client aplications that works fine. The server receive message from client then send back response, the client receive the message and then both of them close the sockets and exit. Now I'm try to create the client program with C# I'm unable to receive the message from the server. The client C# app send the message then C++ Server recieve it correctly but when the server sent back his response the client is unable to receive it. I have tested my server on local virtual machine and on VPS the result was the same. Any idea?I'm having problema to receive message from UDP