Callback from an OCI Catalog with c#

Hi,

as a catalog developer I am trying to callback to an SAP  Netweaver service via the hook url I got.

But I allways get an

401 Unauthorized

Hear is my code:

var request = (HttpWebRequest)WebRequest.Create(uri);

request.Method = "POST";

byte[] dataToPost = Encoding.ASCII.GetBytes("TEST");

using (Stream stream = request.GetRequestStream())
{
    stream.Write(dataToPost, 0, dataToPost.Length);
}

HttpWebResponse response = null;
response = (HttpWebResponse) request.GetResponse();

Please help.