Ruby on Rails

my _form.html.erb was rendered by new.html.erb; from my form:
<%= form_for(@profile) do |f| %>
from firefox->tools->web developer->page source

<form class="new_profile" id="new_profile_0" action="/profiles" accept-charset="UTF-8" method="post"><input name="utf8" type="hidden" value="&#x2713;" /><input type="hidden" name="authenticity_token" value="COqGl7mSxKUqj0cTSqLfPJ4Ov40+Zv8iXhhdteiPDrNL6aD9OI+o0LxKAZ+rCy/zrDO0ROB1+yA3bEaZ8IHfQw==" />

and then when submitted raises ActiveRecord::RecordNotUnique in ProfilesController#create
the create action:
def create
@profile = Profile.new(profile_params)
...
so what's wrong