Sorry if I've misunderstood (and I have no idea what your account name is, nor do I need to know what it is), but all characters have to have a first name AND a last name (and to the best of my knowledge the account name doesn't allow spaces in it).

Again I apologise if I've misunderstood, but if you're trying to create a single name only, that won't work, you need both first and last names.