Reinstall cleanly using this technique: http://www.gnutellaforums.com/333278-post2.html
That means removing all Java, LW, cleaning the system & reinstalling each using the offline installers. If still problems, you will need to tell us a bit more about your set up. I presume you are using windows & not mac or linux lol
You can try changing the compatibility mode to XP or windows 2000/NT & setting to run as admin. These are things which sometimes fix things like this. But there might be a problem with the java on your system at present. Java is well known for corrupt installations over the internet. That's why offline installations are much more reliable.

Yours is an installation problem. I'll move it to that section.