The underlying connection was closed: The server committed a protocol violation. FTP
<p>I was uploading my file using below code,it works fine but some time it throws this error"The underlying connection was closed: The server committed a protocol violation" and stop the process ,when i run it again it upload file with out any issue.</p>

<p>One thing i noticed,if i run this process to upload multiple files then i get this error sometime,if i do less than 5 files then it works fine,any idea where and what i have to look in to it.</p>

<p>I was searchin google nothing found solid solution for this,even one of the msdn blog saying its a bug in FTPwebrequest but not sure.</p>

<p>Environment : C# 4.0, IIS FTP Server.</p>

<p>Thanks in Advance</p>

<pre><code>                FileInfo fileInf = new FileInfo(filename);
                FtpWebRequest reqFTP;

                // Create FtpWebRequest object from the Uri provided
                reqFTP = (FtpWebRequest)FtpWebRequest.Create
                         (new Uri(path + fileInf.Name));


                // Provide the WebPermission Credintials
                 reqFTP.Credentials = new NetworkCredential(user, pwd);

                // By default KeepAlive is true, where the control connection
                // is not closed after a command is executed.
                reqFTP.KeepAlive = false;


                // Specify the command to be executed.
                reqFTP.Method = WebRequestMethods.Ftp.UploadFile;

                // Specify the data transfer type.
                reqFTP.UseBinary = true;
                reqFTP.Timeout = -1;
                reqFTP.UsePassive = true;


                // Notify the server about the size of the uploaded file
                reqFTP.ContentLength = fileInf.Length;

                // The buffer size is set to 2kb
                int buffLength = 4096;
                byte[] buff = new byte[buffLength];
                int contentLen;

                // Opens a file stream (System.IO.FileStream) to read the file
                // to be uploaded
                FileStream fs = fileInf.OpenRead();


                try
                {
                    // Stream to which the file to be upload is written
                    Stream strm = reqFTP.GetRequestStream();

                    // Read from the file stream 2kb at a time
                    contentLen = fs.Read(buff, 0, buffLength);

                    // Till Stream content ends
                    while (contentLen != 0)
                    {
                        // Write Content from the file stream to the FTP Upload
                        // Stream
                        strm.Write(buff, 0, contentLen);
                        contentLen = fs.Read(buff, 0, buffLength);
                    }

                    // Close the file stream and the Request Stream
                    strm.Close();
                    fs.Close();
                }
</code></pre>

<p><strong>Answer</strong></p>

<p>reqFTP.KeepAlive = false; to "True" to get rid of the error in my case.</p>
