Problem going to Rails 3

_step.erb

<li class='step'>  
  <%= sf.hidden_field :id %>
  <%= sf.hidden_field :step_definition_id %>
  <%= sf.hidden_field :position ,:class=>"position"%>
  <%= sf.object.format_with_params { |param| render(:partial=>'scenarios/param' , :locals=>{:param=> param, :sf=>sf})} %>    

  <% if sf.object.new_record? %>
    <%= link_to "Remove", '#', :onclick =>"$(this).parent('.step').remove()" %>
  <% else %>        
    <%= sf.check_box '_destroy' %>
    <%= sf.label '_destroy', 'Remove' %>
  <% end %>
</li>

gistfile1.txt

<%
  @ff = ActionView::Helpers::FormBuilder.new(:scenario, @step.scenario || Scenario.new, @template, {}, proc {} )
  @sf = nil
  @ff.fields_for(:steps, @step,  {:child_index => @next_index}) {|sf| @sf = sf}
  form = render(:partial => 'scenarios/step', :locals => { :sf=> @sf, :step => @step }) 
%>
$("#placeholder<%=@next_index%>").replaceWith("<%= escape_javascript form %>"); 
$("input/.position").each(function(index){$(this).val(index+1);});

ActionView::Template::Error (undefined method fields_for' for nil:NilClass): 2: @sf = nil 3: @fx = ActionView::Helpers::FormBuilder.new(:scenario, @step.scenario || Scenario.new, @template, {}, proc {} ) 4: @form = nil 5: @fx.send(:fields_for, :steps, @step, {:child_index => @next_index}) {|sf| 6: 7: # @form = render(:partial => 'scenarios/step', :locals => { :sf=> sf, :step => @step }) 8: } app/views/steps/new.js.erb:5:in_app_views_steps_new_js_erb___870977895_19276944'