I know it works for many people under Vista, including Kaldran, the guy who programmed it under Vista. Googling for your error message turned this up however, so it may be a bug with Java under Vista:
http://bugs.sun.com/bugdatabase/view...bug_id=6774644
As a workaround you could just use the .jnlp file (or a shortcut thereto) to launch the application.