IE 11 error - Access is denied - XMLHttpRequest

This question appears to be getting a lot of views, so just in case anybody was wondering, I solved this problem by using a setTimeout() on the original AJAX call. E.g:

setTimeout(function() {
        ajaxRequest('save_mark','save_mark_completed',[60962,1284,5]) 
    }, 1);

I'm assuming it's some kind of bug in IE. Just 1 millisecond was all it needed!