This plugin has not been updated by its developer since a long time ago.
It could imply partial or total lack of compatibility with the latest versions of b2evolution.
This is a hack for the conf/hacks.php file. When implemented, this code will allow general search engine referrals to your blog to use the search function of your site to find the item in question. So many times Google or yahoo will list the category or other aggregate of your blog because it is easier for them than individual links. If the search engine refers a direct link, it will pass through. If the link is not specific, it will force the browser to load a page on your site, which will search for the item.