i bought a tytn ii sim free and had no problems signing up to their website. i however signed up when their older site was working, so i don't know whether this has anything to do with it not working for you.
IMO their site is rubbish, they don't offer you anything worth looking at, no ROM updates, no nothing, so its not the end of the world!
Why not try giving them a call if you really want to subscirbe though?