jQuery's ajaxStart and ajaxStop triggering

Question

I have a JS component which has functions progressOn and progressOff to show/hide a progress bar. So far I've done this. It works,but only on the first request.

$(document).ajaxStart(function() {
     layouts["main"].progressOn();
 })
 .ajaxStop(function() {
     layouts["main"].progressOff();
 });

What could be the problem ?