Its hard to say since there have been modifications. The code works out of the box, so it is something with the updates you've made. If you search in the code for $_SESSION['gallery'] =, that should give you all the places where the gallery info is set. It seems like that session variable is never getting set or is getting overwritten. The admin keys off of that variable to get all of the gallery variables.
You might want to start with the admin/js/choosegallery.js file, my guess is the javascript is not firing correctly. I would use firebug on your page and see if there are any JS errors preventing the events from working.
-justin
