CRM 2011 Update Rollup 12 IE10 Compatibility issue

I am working with CRM2011 OnPremise and I have installed UR12, and when I use the application with IE10 i found some issues:

I have installed UR12 and because of my client doesn't want to use other browser that IE, according to the Validation Tool I dont need to need to change any Client Sice Script. That situation is true if I use IE9, the problem appears if I use IE10, even if I use the Compatibility View.

Here is an example of code that works for IE9, but it is not working in IE10 Compatibility View.   

      var accountRequest= "some RetrieveMultipleRequest"

      var request = new XMLHttpRequest();
      request.open("POST", CRM_URL_FULLPATH, false)
      request.setRequestHeader("SOAPAction","http://schemas.microsoft.com/xrm/2011/Contracts/Services/IOrganizationService/RetrieveMultiple");
      request.setRequestHeader("Content-Type", "text/xml; charset=utf-8");
      request.send(accountRequest);

      var resultXml = request.responseXML;
      var xmlDoc = new ActiveXObject("Microsoft.XMLDOM");
      xmlDoc.async = false;
      xmlDoc.loadXML(resultXml.xml);

Like I said before, it works for IE9 but it is not working in IE10, when running IE9 the line "var resultXml = request.responseXML;" leaves resultXml with an object of type IXMLDOMDocument2, using IE10 that line leaves resultXml with an object of type [Object, Document] having an error inside.  

Any ideas of why it is not working? 

Regards,

Sebastian.-