I just installed the plugin for Paperclip and I am getting an error message "undefined method has_attached_file for. Not sure why I am getting this. Here is the full error message.

NoMethodError (undefined method `has_attached_file' for #<Class:0x10338acd0>):
  /Users/bgadoci/.gem/ruby/1.8/gems/will_paginate-2.3.12/lib/will_paginate/finder.rb:170:in `method_missing'
  app/models/post.rb:2
  app/controllers/posts_controller.rb:50:in `show'

For some reason it is referencing the will_paginate gem. From what I can find, it seems that either there is something wrong w/ my PostsController#index or perhaps a previously attempt at installing the gem instead of the plugin (in which case I have read I should be able to remedy through the /config/environments.rb file somehow). I didn't think that previous gem installation would matter as I did it in an old version of the site that I trashed before installing the plugin. In the current version of the site I show that the Table has been updated with the Paperclip columns after migration. Here is my code:

PostsController#index

  def index
    @tag_counts = Tag.count(:group => :tag_name, 
       :order => 'count_all DESC', :limit => 20)
       conditions, joins = {}, :votes
    @vote_counts = Vote.count(:group => :post_title, 
          :order => 'count_all DESC', :limit => 20)
          conditions, joins = {}, :votes


       unless(params[:tag_name] || "").empty?
         conditions = ["tags.tag_name = ? ", params[:tag_name]]
         joins = [:tags, :votes]
       end
       @posts=Post.paginate(
                 :select => "posts.*, count(*) as vote_total", 
                 :joins => joins, 
                 :conditions=> conditions, 
                 :group => "votes.post_id", 
                 :order => "created_at DESC",
                 :page => params[:page], :per_page => 5)
        @popular_posts=Post.paginate(
                 :select => "posts.*, count(*) as vote_total", 
                 :joins => joins, 
                 :conditions=> conditions, 
                 :group => "votes.post_id", 
                 :order => "vote_total DESC",
                 :page => params[:page], :per_page => 3)


    respond_to do |format|
      format.html # index.html.erb
      format.xml  { render :xml => @posts }
      format.json { render :json => @posts }
      format.atom
    end
  end

Post Model

class Post < ActiveRecord::Base

  has_attached_file :photo
  validates_presence_of :body, :title
  has_many :comments, :dependent => :destroy
  has_many :tags, :dependent => :destroy
  has_many :votes, :dependent => :destroy
  belongs_to :user
  after_create :self_vote
      def self_vote
       # I am assuming you have a user_id field in `posts` and `votes` table.
       self.votes.create(:user => self.user)
      end

  cattr_reader :per_page 
    @@per_page = 10

end

/views/posts/new.html.erb

<h1>New post</h1>
<%= link_to 'Back', posts_path %>
<% form_for(@post, :html => { :multipart => true}) do |f| %>
  <%= f.error_messages %>

  <p>
    <%= f.label :title %><br />
    <%= f.text_field :title %>
  </p>
  <p>
    <%= f.label :body %><br />
    <%= f.text_area :body %>
  </p>
  <p>
    <%= f.file_field :photo %>
  </p>

  <p>
    <%= f.submit 'Create' %>
  </p>
<% end %>