Help.. WebClient DownloadData Grabbing Fully Rendered Update Panel, Not "Loading.." message.

I am trying to use
WebClient client = new WebClient();
// Add a user agent header in case the
// requested URI contains a query.
client.Headers.Add("user-agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; .NET CLR 1.0.3705;)");
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