title: jQuery Cross-Domain Ajax JSONP Calls Failing Randomly For Unknown Reasons In Some IE Versions
body: <p>I am making cross-domain Ajax calls using the latest version of jQuery 1.7.1. with a JSONP response.</p>
  
  <p>I have already tested it extensively on:
  Safari, Chrome, Opera, Firefox, IE6 IE7 IE8 IE9 (in compatibility mode and not) on Win XP and Win 7 all of them working flawlessly. Never failing on multiple tests. All of them using the standard default settings with JavaScript and Cookies enabled.</p>
  
  <p>In production, the call very very rarely fails, but i've had several users out of hundreds that have. Probably one out of 50 or 100. I cannot make any sense of this because in all cases:</p>
  
  <ul>
  <li><p>The user did not have problems with non-cross-domain ajax calls using jQuery. (i.e. non-cross-domain calls worked so they must have JavaScript enabled and can support ajax).</p></li>
  <li><p>The user only had problems with cross-domain ajax calls using jQuery. Even after repeated attempts. I.e. the user would either have the problem or not, it would not fail then work or work then fail. Only one or the other.</p></li>
  <li><p>Here are a sample of the user agent strings of the users that where affected:</p>
  
  <p>Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0; FunWebProducts)</p>
  
  <p>Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; GTB7.2; .NET CLR 2.0.50727; .NET CLR 3.5.30729)</p>
  
  <p>Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; CPNTDF; ibrytetoolbar_playbryte; .NET4.0C)</p></li>
  </ul>
  
  <p>It only seems to affect IE, i've never had the problem with other browsers.</p>
  
  <ul>
  <li><p>The problem goes away if they use a different browser, i told them to install Chrome.</p></li>
  <li><p>The problem cannot be connection, computer or OS based as changing browsers worked.</p></li>
  </ul>
  
  <p>I can only rule out that it must be a setting that can only be found on IE. Has anyone had this issue? Does anyone have an idea of which IE setting might be blocking cross-domain Ajax calls with a JSONP response.</p>
  
  <p>It cannot be the usual AJAX/JSONP/Cross-domain problems, since these problems do not occur when the browsers are set to default, and also because i've already done it the proper way:
  * timestamp string on the end to stop super caching
  * JSONP response
  etc etc</p>
  
  <p>I can confirm that the call is not firing at all.</p>