Hello Rob,

From your description, when you're using the HttpWebrequest component to
programmatically request some web pages, you get some IOException indicate
that can not read data. Also, those pages can be correctly requested
through standard webbrowser, correct?

As for the Exception, have you debugged into the code to see at which line
does the exception occur?  Since the error message said can not read data
..  I assume the exception occur after the " objRequest.GetResponse();"
call and raised at the "ReadToEnd" call, is this the case?  If so, it seems
the server-side has terminate the connection intermediately.  

Does this problem frequently occur when you use HttpWebRequest class to
request the pages? According to my research, there are several possible
issues for such error:

** the request's processing time has exceed the server-side application's
timeout setting and the server close the connection.

** The server-side terminate the current connection due to some reason(in
order to free the thread to process other task)

** the server instance encounter some exception and recycle the service
which cause the current connection be terminated.

Also, since you said that other browser and utility can correctly download
the page, I suggest you use some trace tools to capture the HTTP request
and response messages generated by both your application(that use
httpwebrequest) or webbrowser and compare them(mostly it is the http header
that may differ between the two cases).  You can consider some simple tools
like the "trace utility" in soap toolkit 3.0 or the tcptrace windows
version:

#SOAP Toolkit 3.0
http://www.microsoft.com/downloads/details.aspx?familyid=c943c0dd-ceec-4088-
9753-86f052ec8450&displaylang=en

#TcpTrace
http://www.pocketsoap.com/tcptrace/

In addition, here is a test program which can programmatically request the
page url you posted(I add some addiontal headers in the webrequest object).
You can refer to it and see whether it also works for you:

===================cs code=====================
class Program
   {
       static void Main(string[] args)
       {
           try
           {
               Run();
           }
           catch (Exception ex)
           {

               Console.WriteLine(ex.ToString());
           }
       }

       static void Run()
       {
           string url =
"http://www.chemistry.org/portal/a/c/s/1/professionals.html";
         
           string result = null;
           HttpWebRequest req = null;
           HttpWebResponse rep = null;

           req = WebRequest.Create(url) as HttpWebRequest;

           req.Method = "GET";
           req.UserAgent = "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT
5.1; InfoPath.2; .NET CLR 2.0.50727; .NET CLR 1.1.4322; .NET CLR
3.0.04506.30)";
         

           req.Accept = "image/gif, image/x-xbitmap, image/jpeg,
image/pjpeg, application/x-shockwave-flash, application/vnd.ms-excel,
application/vnd.ms-powerpoint, application/msword, application/xaml+xml,
application/vnd.ms-xpsdocument, application/x-ms-xbap,
application/x-ms-application, */*";
           req.Headers[HttpRequestHeader.AcceptLanguage] =
"en-us,zh-CN;q=0.8,es-ES;q=0.5,fr-FR;q=0.3";

         
         

           rep = req.GetResponse() as HttpWebResponse;

           Console.WriteLine("status code: {0},contenttype:{1},
length:{2}", rep.StatusCode, rep.ContentType, rep.ContentLength);

           
           using (System.IO.StreamReader sr =

           new System.IO.StreamReader(rep.GetResponseStream()))
           {

               result = sr.ReadToEnd();

           }

           Console.Write(result);

       }
   }
============================

Hope this helps.

Sincerely,

Steven Cheng

Microsoft MSDN Online Support Lead



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Thus wrote Rob,

[...]

Rob, I've got no problem loading that page using a .NET based HTTP client.
You should try to include common HTTP headers such as Accept, Accept-Language,
and User-Agent in your request to make sure you don't confuse the web application
-- it may rely on these headers to work properly

Cheers,