Problems adding fields in nested form through jQuery form railscasts episode

i have followed the railscasts episode on nested forms(part 1 and 2) and having difficulty with adding fields using jquery, however when i click the remove fields link, the field gets removed. Here is the code.
In my question model i have

class Question < ActiveRecord::Base
has_many :tags, :class_name => "Tag", :dependent => :destroy, :foreign_key => "question_id"
accepts_nested_attributes_for :tags, :reject_if => lambda { |a| a[:keyword].blank? }, :allow_destroy => true

In my tag model i have

class Tag < ActiveRecord::Base
    attr_accessible :keyword, :question_id
    belongs_to :question, :class_name => "Question", :foreign_key => 'question_id'
end

In my question form i have

<%= form_for @question, :url => { :controller => "questions", :action => "create" } do |f| %>
    <%= f.label(:name, "Request Question:") %>&nbsp;&nbsp;
    <%= f.text_field(:name, :size => 72, :maxlength => 120) %><br />
    <%= f.fields_for :tags, :url => { :controller => "tags", :action => "create" } do |builder| %>
        <%= render "tag_fields", :f => builder %>
    <% end %>
    <p><%= link_to_add_fields "Add new tag", f, :tags %></p>
<% end %>

In my tag_fields partial

<p class="fields">
    <%= f.label(:keyword, "Keywords:") %>&nbsp;&nbsp;
    <%= f.text_field(:keyword, :size => 20, :maxlength => 25) %>
    <%= link_to_remove_fields "remove", f %>
</p>

In application_helper.rb

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

Then finally in my application.js

function remove_fields(link) {
    $(link).prev("input[type=hidden]").val("1");
    $(link).closest(".fields").hide();
}

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

I have checked to see if files are included in page source. The jquery works because other parts of my app are working. I do not get any error when i click add new tag. I have looked at other solutions, but none work for me. I cannot seem to add a field. Thanks for the help