Element.insert_html is not function

Hi

I have created the application by following the railcast video

http://railscasts.com/episodes/74-complex-forms-part-2

However I am getting this error when I click "add element"

RJS error:

TypeError: Element.insert is not a function

and then

Element.insert("docs", { bottom: "<div class=\"doc\">\n\n
Doc: <input .....etc

I have added the <%= javascript_include_tag :defaults %> in layout
files also

here is my rjs line
<%= render :partial => 'task', :collection => @project.tasks %>

please help me in this regards.

Hi,

Please verify that all included javascript files get successfully
loaded into your html page.

Hi,

    I inserted required java script files in my html page that is
new.html.erb

Plaese verify the file...

#Projects/new.html.erb

<% form_for :project, :url => projects_path do |f| %>

  <p>
    Name: <%= f.text_field :name %>
  </p>

  <div id="tasks">
    <%= render :partial => 'task', :collection => @project.tasks %>
  </div>

  <%= link_to_function "Add a Task" do |page|

    page.insert_html:bottom, :tasks, :partial => 'task', :object =>
Task.new
  end %>

  <p><%= submit_tag "Create Project" %></p>
<% end %>

#My controller i.e projects

class ProjectsController < ApplicationController

def index
@projects = Project.find(:all)
end

def new
  @project = Project.new
@project.tasks.build

end

def create
  @project = Project.new(params[:project])
  if @project.save
    flash[:notice] = "Successfully created project and tasks."
    redirect_to projects_path
  else
    render :action => 'new'
  end
end

def edit
  @project = Project.find(params[:id])
end

def update
  params[:project][:existing_task_attributes] ||= {}

  @project = Project.find(params[:id])
  if @project.update_attributes(params[:project])
    flash[:notice] = "Successfully updated project and tasks."
    redirect_to project_path(@project)
  else
    render :action => 'edit'
  end
end

end