Menu links not working — how to debug?

A couple upgrades ago, the links in my menus stopped working, and I’m not sure how to debug this. http://www.thegrotonline.com

The links appear to be hot, in that the “link” cursor displays on hover, and the destination URL displays in different browser status lines. But when the menu item is clicked, nothing happens.

Any thoughts on how to ID what’s wrong?

Thanks for any ideas!