FileUpload ASP.NET is not authorized to access the requested resource.

I have changed the application folder permission on my IIS 6 manager to groups network services, network (added full control/access). Here is my FileUpload code
string extension1 = Path.GetExtension(FileUpload1.PostedFile.FileName).ToLower();

            ArrayList attachments = new ArrayList();

            if (FileUpload1.HasFile && (
                extension1 == ".pdf" || extension1 == ".doc" ||
                extension1 == ".docx" || extension1 == ".xls" ||
                extension1 == ".xlsx" || extension1 == ".gif" ||
  &n ...