For Windows (sorry, don't know about other OSs):

What version of Java are you using? Update Java & use the JRE offline installer here. Remove your current Java version before you install the new one.
http://java.sun.com/javase/downloads/index_jdk5.jsp

If that doesn't help, delete LW's preferences folder (make sure LW's properly closed first). See points 2 & 3 here. If you've used an older version of LW in the past, you could have a folder in both locations. This will kill your settings within options, you'll have to go back thru & reset things afterwards
Fixes for LimeWire

And if that doesn't work, try Java 1.6. Same deal as before with the JRE offline installer & removing old version.
http://java.sun.com/javase/downloads/index.jsp