Nostalrius Begins - Quality wow vanilla realm (1.12)

It just always says ''Please fill the form correctly'', no matter how I change my password, Username or email.

Are you using any special characters in either your account name or password (E.g.: spaces, . ! ~ # $ % &, etc.)? Or just numbers and letters only? Try creating an account in a different web browser (E.g.: Chrome, Firefox, Opera, Internet Explorer, Safari, etc.).