Well, could be a Java issue or a compatibility issue.
Update your Java using the JRE offline installer of the newest version from here:
http://java.sun.com/j2se/1.5.0/download.jsp
Make sure you have uninstalled all other versions of Java and rebooted before and after installing it.
As for the compatibility. Right-click the LW icon on your desktop and go to Properties. There you choose the Compatibility tab and change the compatibility to Windows NT or Windows 2000.