First of all, make sure youre downloading it from
http://code.google.com/p/blacktree-alchemy/downloads/list and not the Blacktree site, as thats where all the current work is being done on it.
Second of all, thats caused by incompatible plugins. Go to ~/Library/Application Support/Quicksilver/PlugIns and delete them all. Then add them back, one by one. When QS stops working, youll know you found the culprit(s). Simply uninstalling the incompatible plugins will make it work again (Ive been using it every day for a month now).