Version 1.0.12 for windows will not complete registration and will not start the program. 1.0.11 works fine.
That's very odd. The program should start even if the registation fails. Have you tried reinstalling java from the sun website? That often helps.
Incidentally, for the first two weeks of november 2005, the server-side of the registration process was broken, so all of the registration attempts for that period would have failed. I just noticed today and fixed it, so it should work again.