In some cases the window.XMLHttpRequest has a true return at ie7 but the window.XMLHttpRequest() still can't be created.

If you put the return new window.XMLHttpRequest() in a try catch block and on error you return the activexobject instead of the xmlhttprequest then everything is working fine.

This is the code from jquery:

xhr: window.XMLHttpRequest && (window.location.protocol !== "file:" || !window.ActiveXObject) ?

function() {

return new window.XMLHttpRequest();

} :

function() {

try {

return new window.ActiveXObject("Microsoft.XMLHTTP");

} catch(e) {}

},