Getting error "(501) Syntax error in parameters or arguments"

Question

I have created an FTP upload/download application for my place of employment.  Everything was working fine until I started receiving the following error: "The remote server returned an error. (501) Syntax error in parameters or arguments".  I have tried searching the web for related issues and found some people having the same problem.  There is even a post on this site where someone was having the same issue.  However, their fix did not work for me.  They stated that all they did was changed KeepAlive to false.  I already set mine as false.

Here is my code:

    public void UploadFile(string srcfile, string destfile)
    {
      if (srcfile == "") { WriteLog("File name can not be blank!", "Warning"); return; }

      FileInfo fi = new FileInfo(srcfile);

      if (!fi.Exists) { WriteLog("File name \"" + fi.FullName + "\" could not be found!", "Warning"); return; }

      if (IPAddress.Substring(IPAddress.Length - 1, 1) != "/")
        destfile = IPAddress + "/" + destfile;
      else
        destfile = IPAddress + destfile;

      if (IPAddress.Substring(0, 6) != "ftp://") destfile = "ftp://" + destfile;

      try
      {
        ftp = (FtpWebRequest)FtpWebRequest.Create(destfile);
        ftp.Credentials = new NetworkCredential(UserID, Password);
        ftp.KeepAlive = false;
        ftp.UseBinary = true;
        ftp.Method = WebRequestMethods.Ftp.UploadFile;

        byte[] fContent = new byte[fi.Length];

        using (FileStream fr = fi.OpenRead())
          fr.Read(fContent, 0, Convert.ToInt32(fi.Length));
        using (System.IO.Stream sw = ftp.GetRequestStream())
          sw.Write(fContent, 0, fContent.Length);

        FtpWebResponse fresp = (FtpWebResponse)ftp.GetResponse();
        WriteLog("Successfully uploaded file \"" + srcfile + "\". " + fresp.StatusDescription, "Success");
      }
      catch (WebException wex)
      { throw new WebException("ERROR 108001: " + wex.Message, wex.Status); }
      catch (Exception ex)
      { throw new Exception("ERROR 108002: " + ex.Message); }
    }

The program works fine for several of the sites that I try, but it seems one of my hosts has an issue.  I have verified the "destfile" string and made sure that the uri is not malformed, so now I am at a loss.  If anyone has any suggestions I am open to hearing them.

Thanks

Answer 1

Something I neglected to put in my first post is that I am attempting to upload a file to an AS400 system.

I used WireShark to try and figure out what my issue is, and I am left with a bigger mystery than before.  The response that WireShark recorded from the server was "Character (/) not allowed in object name".  I tried taking out the IP address and everything and just leaving the filename, but when it attempts to do the FtpWebRequest.Create method I get an error that says invalid uri.