uploading to HTTP file

I am developing a program which will upload a file to a similar website  http://www.zoneedit.com/auth/ ...

below is the code...
           
try
{
 System.Net.ServicePointManager.CertificatePolicy = new MyPolicy();
        WebClient Client = new WebClient();
        Client.Credentials = new NetworkCredential("user", "Password", "https://dts.website.com");
        Client.UploadFile("https://dts.website.com/upload_folder", "c:\myfile.txt");
}
catch (Exception expx)
{
        MessageBox.Show(expx.Message);
}
I was given a user name & password by the administrator of the above website, but my program returns "error 401 Unauthorized"
username & password will work only f i'll open thier website in the internet Explorer but not from my program.
The administrator told me that the above username & password have enough rights to upload into the given website. 
did miss somthing in my code?
 

Hey,
  You cancel the authorization dialog box, you will be redirected to another page, where you to click on another link (free web page hosting link).
In that page cilck on Lost your password, or secure login. They might mail you new username password.