Not sure if this will help anyone else but I upgraded from 3.6 to 3.7.1 and Jaikoz would not start up. My java version is 1.6 build 20 32bit (the latest version I believe). After much head scratching I deleted my \users\\Jaikoz directory and it started right up. Of course I had to reinstall my license key.
Paul, let me know if I was just being stupid or of there is info you want to help diagnos the problem.