title: webdriver.switchTo().defaultContent() triggers System.InvalidOperationException in IE9
body: <p>I'm using Selenium 2.15 to drive IE9. Overall, it's been working fine. I've got a weird scenario where a: <code>driver.SwitchTo().DefaultContent()</code> is triggering a <code>System.InvalidOperationException</code> (the message is "<code>Unable to get browser (NoSuchDriver)</code>"). I'm quite certain the browser is up and running, and has in fact driven to the content requested. The content in question is a single line HTML doc:</p>
  
  <pre><code>&lt;div id='me'&gt;simple page&lt;/div&gt;
  </code></pre>
  
  <p>Is there any reason why SwitchTo().DefaultContent() would fail on such a page?</p>