Error :The remote server returned an error: (401) Unauthorized

Shouldn't you be providing the credentials for your site, instead of passing the DefaultCredentials?

Something like request.Credentials = new NetworkCredential("UserName", "PassWord");

Also, remove request.UseDefaultCredentials = true; request.PreAuthenticate = true;

I add credentials for HttpWebRequest.

myReq.UseDefaultCredentials = true;
myReq.PreAuthenticate = true;
myReq.Credentials = CredentialCache.DefaultCredentials;