在C＃中使用FTP发送文件

我试图发送使用ftp文件。我有以下的code：

I'm trying to send a file using ftp. I have the following code:

string server = "x.x.x.x";  // Just the IP Address 

FileStream stream = File.OpenRead(filename);
byte[] buffer = new byte[stream.Length];

WebRequest request = WebRequest.Create("ftp://" + server);
request.Method = WebRequestMethods.Ftp.UploadFile;            
request.Credentials = new NetworkCredential(username, password);

Stream reqStream = request.GetRequestStream(); // This line fails
reqStream.Write(buffer, 0, buffer.Length);
reqStream.Close();

但是，当我运行它，我得到以下错误：

But when I run it, I get the following error:

请求的URI是该FTP命令无效。

The requested URI is invalid for this FTP command.

请谁能告诉我为什么吗？我使用这个错误？

Please can anyone tell me why? Am I using this incorrectly?