When using MooTools 1.11 the event object target property can not be read by IE. The way to correct this is to use the following…
var target = $(e.target || e.srcElement);
Here it is with surrounding code…
$('elementId').addEvent('click', function(e) { var target = $(e.target || e.srcElement); if(target.checked){ //do something here } else { //do something here } });

Thank-you thank-you thank-you!! This helped perfectly to solve my problem of IE not reading the target property. You have helped to save me a lot of work.