Hi,

I am using the ms ajax library with an update panel in a user web control.
The update panel contains two linked dropdownlists whose contents are
modified (on autopostback) depending on the selection in eachother. This
also modifies the imageurl of an image control, also in the same update
panel.

This works fine locally, but as soon as I host it on our webserver (outside
our firewall) and access it from inside our firewall, it throws an error:
"Sys.WebForms.PageRequestManagerParserErrorException: The message received
from the server could not be parsed...". It works fine when called from a
browser on the webserver itself.

I have discovered this is down to our firewall stripping out the "unknown
header" X-MicrosoftAjax, which is added to the web request by the
ScriptManager during the postback. This causes the server to think it's a
full-page postback and sends back the entire page in the response, not just
the partial update. The page works fine when I remove the "unknown headers"
filter from our firewall.

This will also happen to other visitors who have similar filters on their
firewalls and, I assume, must affect *every* website that uses ajax update
panels.

I have only found one solution so far for this, which involves BeginRequest
in global.asax and requires adding the header back in to the collection if
it is found to be missing on an ajax partial postback, (code below).

However, I am receiving the error "Operation is not supported on this
platform." at System.Web.HttpHeaderCollection.Add(String name, String
value).

Does anyone have any idea how to get around either of these problems?

Kind regards

Chris Chamberlain
Head of IT
VEF (UK) Ltd
www.vefuk.com
------------------------------------------------------------------

Code (found on http://forums.asp.net/p/1144748/1850717.aspx):

On the page with the UpdatePanel...
<script type="text/javascript>
function beginRequest(sender, args) {
  var r=args.get_request();
  if (r.get_headers()["X-MicrosoftAjax"])
  {
   b=r.get_body();
   var a="__MicrosoftAjax=" +
encodeURIComponent(r.get_headers()["X-MicrosoftAjax"]);
   if (b!=null && b.length>0)
   {
b+="&";
   }
   else
b="";
   r.set_body(b+a);
  }
}
Sys.WebForms.PageRequestManager.getInstance().add_beginRequest(beginRequest);
</script type="text/javascript>

And in BeginRequest (Global.asax or in an HttpHandler).....
HttpRequest request = HttpContext.Current.Request;
if (request.Headers["X-MicrosoftAjax"] == null &&
request.Form["__MicrosoftAjax"] != null)
{
  request.Headers.GetType().InvokeMember("MakeReadWrite",
System.Reflection.BindingFlags.InvokeMethod |
System.Reflection.BindingFlags.NonPublic |
System.Reflection.BindingFlags.Instance, null, request.Headers, null);
  request.Headers.Add("X-MicrosoftAjax", request.Form["__MicrosoftAjax"]);
  request.Headers.GetType().InvokeMember("MakeReadOnly",
System.Reflection.BindingFlags.InvokeMethod |
System.Reflection.BindingFlags.NonPublic |
System.Reflection.BindingFlags.Instance, null, request.Headers, null);
}