无法建立与远程服务器的连接

Question

我想将文件从Windows Server 2012 R2下载到本地计算机。文件路径：E:\Update。

我试过这段代码：

string localPath = @"C:\Update\";
string fileName = "update.xml";

try
{
    var requestFileDownload = (FtpWebRequest)WebRequest.Create("ftp://111.111.111.111/E:/Update/" + fileName);
    requestFileDownload.Method = WebRequestMethods.Ftp.DownloadFile;

    FtpWebResponse responseFileDownload = (FtpWebResponse)requestFileDownload.GetResponse();

    using (Stream responseStream = responseFileDownload.GetResponseStream())
    {
        using (FileStream writeStream = new FileStream(localPath + fileName, FileMode.Create))
        {
            int Length = 2048;
            Byte[] buffer = new Byte[Length];
            int bytesRead = responseStream.Read(buffer, 0, Length);

            while (bytesRead > 0)
            {
                writeStream.Write(buffer, 0, bytesRead);
                bytesRead = responseStream.Read(buffer, 0, Length);
            }
        }
    }       

    System.Windows.Forms.MessageBox.Show("Downloaded..." );
}
catch (Exception ex1)
{
    System.Windows.Forms.MessageBox.Show("Downloading error..."+ex1.Message);
}

但是我收到了错误

  

无法建立与远程服务器的连接。

什么可能导致此错误消息？