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!