title: ASP.NET UpdatePanel Error htmlfile: Unknown runtime error, updatePanelElement.innerHTML=rendering
body: <p>I get this error when debugging my ASP.NET web application after I trigger an UpdatePanel:</p>
  
  <p><img src="https://i.stack.imgur.com/CqrGC.gif" alt="ASP.NET htmlfile: Unknown runtime error updatePanelElement.innerHTML=rendering"></p>
  
  <p>htmlfile: Unknown runtime error</p>
  
  <p>and "updatePanelElement.innerHTML=rendering" is highlighted in a ScriptResource.axd file.</p>