I recently tried to upgrade to Stuffit v.11.0 from v.10.0 on my Mac running Mac OS X 10.4. When launching DropStuff, multiple processes started kicking in, which prevented DropStuff from being launched. After checking the logs, I noticed that it could not replace the Stuffit.Framework folder. To fix this, I removed StuffIt.framework and StuffItSupport.framework from the /Library/Frameworks directory.
When I relaunched Dropstuff, new copies of StuffIt.framework and StuffItCore.framework were created automatically. Both Stuffit Expander and DropStuff are working fine now.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20061115022039145