solved it, the whole problem was the request method, it needed a post not a get, i figured it out by using wireshark software.
var uri = new Uri("");
var downloader = new BackgroundDownloader();
downloader.SetRequestHeader("Range", "bytes=0-");
downloader.Method = "POST";
downloader.SetRequestHeader("Content-Type", "multipart/form-data; boundary=----WebKitFormBoundaryx5pLn3bHAS5Q8Ns5");
downloader.ServerCredential = new Windows.Security.Credentials.PasswordCredential()
{
UserName = signin.theusername,
Password = signin.thepassword
};