HttpWebRequest with FormsAuthentification application

Hi,   i'm using HttpWebRequest to do a call to my SSRS Server to get a PDF exportation of my report to attach it to an email.   Here's the code i'm using. ------------------------------------------------------------  Dim reportURL As String = "http://server/ReportServer/Pages/ReportViewer.aspx?%2fRAM%2fBooking&rs:Command=Render&rs:Format=PDF" Dim request As WebRequest   reportURL += "&idbooking=" + Session("idbooking").ToString   'main booking request = System.Net.HttpWebRequest.Create(reportURL + "&idref=0") request.Credentials = System.Net.CredentialCache.DefaultNetworkCredentials 'Make a new attachment with the the stream from the response ...