Try deleting your LW Preferences found here: /Users/your_username/Library/Preferences/LimeWire

Try the Java & other hints here: icon bouncing in Dock (click on link) Go to the bottom of that thread & you'll find some hints about how to overcome the installation of Java issue. ie: You get the "null" message in the Apple installer when a OS X thinks a more recent version is installed. Double-click the harddrive icon, open the Library, open the Receipts folder, then find the file: Install Java142Update2.pkg, delete it and try again.