Reason for the registration being closed is cause so many people make accounts and it makes the server mad that so many people are using it at the same time. So therefor, there is a registration limit and is set up on a random opening schedule.
So if you want a account of your own then you just need to check on the Feral Heart site periodically. When it does open, it only stays open for about 2-3 hours then it closes.
Reasons for why it's closed is already provided above by Shally.