a is undefined

a is undefined

This one is over my head!  I keep getting a sporadic "a is undefined" error from jQuery.  I'm sure the culprit is in my code, not jQuery, but Firebug keeps pointing me to the library.

Anyway, the issue can be replicated here: http://interactive.mellemallc.com by simply clicking around quickly on the links in the sidebar.

Also worth noting, I've commented out virtually every line in my script to find out where the culprit may lie, and I've found that when I comment out the simple line calling the jQuery metadata plugin, that stops the error from happening - though I can't figure out why it would be caused by that.  The line I'm referring to is:

var jdata = $li.metadata({ type: 'attr', name: 'jdata' });

Thanks for any suggestions,
Brian