Strange AJAX/403 Bug

I'm working on this site for a client: http://50.28.69.176/~mendonca/collections.php

And I'm using jQuery to fire AJAX c开发者_如何学Calls to view the enlarged images in a pop-in (Facebook style). But, I've noticed that when I use the buttons below the image to rapidly click through the image set I hang Safari or Chrome. Then when I try to refresh the page I get a 403 error.

Oddly, this doesn't happen in FF.

So, I'm not sure if this is my server or ... what it is.

Any help would be appreciated. Has anyone else ever run into this?