nested form error

_form.html.erb

<%= form_for(@task) do |f| %>
  <% if @task.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(@task.errors.count, "error") %> prohibited this task from being saved:</h2>

      <ul>
      <% @task.errors.full_messages.each do |msg| %>
        <li><%= msg %></li>
      <% end %>
      </ul>
    </div>
  <% end %>

  <div class="field">
    <%= f.label :name %><br />
    <%= f.text_field :name %>
  </div>
  <%= link_to_add_fields "Add timer", f, :clock_ins %>
  <% f.fields_for :clock_ins do |builder| %>
    <%= render "clock_in_fields", :f => builder %>
  <% end %>
  <div class="actions">
    <%= f.submit %>
  </div>
<% end %>

application.js

// Place your application-specific JavaScript functions and classes here
// This file is automatically included by javascript_include_tag :defaults

function remove_fields (link) {
  $(link).previous("input[type=hidden]").value = "1";
  $(link).up(".fields").hide();
}

function add_fields(link, association, content) {
  var new_id = new Date().getTime();
  var regexp = new RegExp("new_" + association, "g")
  $(link).up().insert({
    before: content.replace(regexp, new_id)
  });
}

application_helper.erb

# Methods added to this helper will be available to all templates in the application.
module ApplicationHelper
  def link_to_remove_fields(name, f)
    f.hidden_field(:_destroy) + link_to_function(name, "remove_fields(this)")
  end
  
  def link_to_add_fields(name, f, association)
    new_object = f.object.class.reflect_on_association(association).klass.new
    fields = f.fields_for(association, new_object, :child_index => "new_#{association}") do |builder|
      render(association.to_s.singularize + "_fields", :f => builder)
    end
    link_to_function(name, h("add_fields(this, '#{association}', '#{escape_javascript(fields)}')"))
  end
end