无法上传文件到FTP.net

从生产服务器在ftp上创建文件有问题。以下代码在我的开发服务器上运行良好，但是当我将代码移动到我购买主机的站点上的生产服务器时，它会给出错误

string fullname = Convert.ToString(TxtBx_FullName.Text);
if (FU_Img.HasFile)
{
    string ftpUrl = "";
    HttpPostedFile userPostFile = FU_Img.PostedFile;
    string uploadUrl = @"ftp://abc/upload/u" + fullname;
    string uploadFileName = Path.GetFileName(FU_Img.FileName);
    uploadFileName = "image." + uploadFileName.Split('.')[1];

    Stream streamObj = userPostFile.InputStream;
    Byte[] buffer = new Byte[userPostFile.ContentLength];
    streamObj.Read(buffer, 0, buffer.Length);
    streamObj.Close();
    streamObj = null;
    // FtpWebResponse CreateForderResponse;
    if (!GetAllFilesList(uploadUrl, "xyz", "******"))
    {
         FtpWebRequest ftp = (FtpWebRequest)FtpWebRequest.Create(uploadUrl);
         ftp.Method = WebRequestMethods.Ftp.MakeDirectory;
         ftp.Credentials = new NetworkCredential("xyz", "******");
         FtpWebResponse response = (FtpWebResponse)ftp.GetResponse();
    }
    //if (CreateForderResponse.StatusCode == FtpStatusCode.PathnameCreated)

    ftpUrl = string.Format("{0}/{1}", uploadUrl, uploadFileName);
    FtpWebRequest requestObj = FtpWebRequest.Create(ftpUrl) as FtpWebRequest;
    requestObj.KeepAlive = false;
    requestObj.UseBinary = true;
    requestObj.Method = WebRequestMethods.Ftp.UploadFile;
    requestObj.Credentials = new NetworkCredential("xxxx", "xxxxxx");
    Stream requestStream = requestObj.GetRequestStream(); <----- error
    requestStream.Write(buffer, 0, buffer.Length);
    requestStream.Flush();
    requestStream.Close();
    requestObj = null;

误差

堆栈跟踪

[WebException: The remote server returned an error: (550) File unavailable (e.g., file not found, no access).]
   System.Net.FtpWebRequest.SyncRequestCallback(Object obj) +341
   System.Net.FtpWebRequest.RequestCallback(Object obj) +23
   System.Net.CommandStream.Dispose(Boolean disposing) +19
   System.IO.Stream.Close() +20
   System.IO.Stream.Dispose() +10
   System.Net.ConnectionPool.Destroy(PooledStream pooledStream) +188
   System.Net.ConnectionPool.PutConnection(PooledStream pooledStream, Object owningObject, Int32 creationTimeout, Boolean canReuse) +118
   System.Net.FtpWebRequest.FinishRequestStage(RequestStage stage) +655
   System.Net.FtpWebRequest.GetRequestStream() +795
   MentorMentee.SignUp.signup.Btn_Preview_Click(Object sender, EventArgs e) +954
   System.EventHandler.Invoke(Object sender, EventArgs e) +0
   System.Web.UI.WebControls.Button.OnClick(EventArgs e) +9553178
   System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +103
   System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +10
   System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13
   System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +35
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1724

我发现是假的属性KeepAlive，但没有工作。我哪里做错了?

private bool FtpUpload(FileUpload file, string ftpServer, string username, string ftpPass, string domainName = "")
    {
        // ftp://domain'user:password@ftpserver/url-path
        // If you are a member of a domain, then "ftp://domain-name'username:password@url-path" may fail because the backslash (') is sent in as a literal character and Internet Explorer incorrectly looks for a file instead of parsing a Web address. Changing the backslash (') in the domain-name'username to domainname%5Cusername works correctly.
        try
        {
            string ftpAddres;
            if (domainName != string.Empty)
                ftpAddres = "ftp://" + domainName + @"%5C" + username + ":" + ftpPass + "@" + ftpServer + "/" + file.FileName;
            else
                ftpAddres = "ftp://" + username + ":" + ftpPass + "@" + ftpServer + "/" + file.FileName;
            using (var webClient = new System.Net.WebClient())
            {
                webClient.UploadData(new Uri(ftpAddres), file.FileBytes);
            }
        }
        catch (Exception e)
        {
            throw new Exception(e.Message, e);
        }
        return true;
    }