title: Intermittent Async_ExceptionOccurred errors in a Silverlight 4 app
body: <p>One of our users received the following unexpected error yesterday whilst using our Silverlight app:</p>
  
  <p>[Async_ExceptionOccurred]
  Arguments:
  Debugging resource strings are unavailable.  Often the key and arguments provide sufficient information to diagnose the problem.</p>
  
  <p>Any idea how I start to investigate this?  The problem is intermittent and has so far occurred twice.  We are not using a clientaccesspolicy.xml file as the services and web app are on the same server.  I have looked at the IIS logs for the time the user received the error but cannot see any obvious problems.</p>
  
  <p>Where should I go from here?  I can hardly ask the user to install Fiddler as the problem is very infrequent.  </p>