title: Why does EndGetResponse throw ArgumentNullException?
body: <p>The following line of code throws an ArgumentNullException under Chrome and Firefox in silverlight.  I am using HttpWebRequest to post a file to the server.  The exception doesn't happen in IE and only happens when I am uploading a larger file (5mb).  Under IE it works just fine.  I didn't see any reason in the documentation why the code would throw this exception.</p>
  
  <pre><code>//note that asyncResult is not null
  response = (HttpWebResponse)request.EndGetResponse(asyncResult);
  </code></pre>
  
  <p>Here is the stack trace from the exception:</p>
  
  <pre><code>at System.Net.Browser.ClientHttpWebRequest.InternalEndGetResponse(IAsyncResult asyncResult)
  at System.Net.Browser.ClientHttpWebRequest.&lt;&gt;c__DisplayClass5.&lt;EndGetResponse&gt;b__4(Object sendState)
  at System.Net.Browser.AsyncHelper.&lt;&gt;c__DisplayClass2.&lt;BeginOnUI&gt;b__0(Object sendState)
  </code></pre>
  
  <p>and inner exception:</p>
  
  <pre><code>at System.Net.Browser.AsyncHelper.BeginOnUI(SendOrPostCallback beginMethod, Object state)
  at System.Net.Browser.ClientHttpWebRequest.EndGetResponse(IAsyncResult asyncResult)
  at DC.FileUpload.FileUpload.&lt;&gt;c__DisplayClassc.&lt;UploadFileEx&gt;b__a(IAsyncResult asyncResult)
  </code></pre>