So, I had the same problem as well. It worked fine the first time that I installed it. However, when I upgraded wp core to v. 3.3.2., the bootstrap-dropdown.js, which is located in the folder: (your-website-url/plugin/all-in-one-event-calendar/themes-ai1ec/vortex/js/bootstrap-dropdown.js ), was not loaded.
Add the code below to your site header.php and refresh, and that should do the trick.
<script src=”https://www.your-site-url.com/wp-content/plugins/all-in-one-event-calendar/themes-ai1ec/vortex/js/bootstrap-dropdown.js”></script>
_G
