OK, having placed the original files back in I can the problem. The collapse/expand does work, however it is when it tries to reload the page afters that it goes wrong because it redirects the user to...
http://www.mkivsupra.net/pp-classifieds/misc.php.php
Note the double .php at the end. Taking one of those off loads the page correctly with the category expanded or collapse as expected. You can test this using the logins I've PM'd you for the permissions problem.