post.rb

#post_controller.rb
class PostController < ApplicationController
  filter_access_to :all
  before_filter :login_required


  def add
  @posts=Post.new(params[:posts])
  @posts.author = current_user
  if request.post? and @posts.save
    flash[:notice]='Post Published'
  end
  def all
    @post=Post.find(:all)
  end
  end
end
#all.rhtml
<div id="content-header">
  <img src="/images/manage_news/manage_news_logo.png" />
  <h1>Forum / Blog / Q & A</h1>
  <h3>Latest Knowledge Thirst</h3>
  <div id="app-back-button">
    <%= link_to_function image_tag("/images/buttons/back.png",:border => 0), "history.back()" %>
  </div>
</div>

<div id="page-yield">

  <% unless flash[:notice].nil? %>
    <p class="flash-msg"> <%= flash[:notice] %> </p>
  <% end %>

  <div id="all_news">
  <ul>
  <% for posts in @post %>
  	<li><%= link_to posts.title, :controller=> 'post', :action=>'view',:id=>posts.id %>
  <%end%>
  </ul>
  </div>

</div>

#error
You have a nil object when you didn't expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.each

But i have checked in db i have one value and i also tried 
kracekumar@kracekumar-laptop:/var/www/admin$ ruby script/console
Loading development environment (Rails 2.3.5)
/var/lib/gems/1.8/gems/rails-2.3.5/lib/commands/console.rb:45: warning: Insecure world writable dir /opt/ns in PATH, mode 040777
>> p=Post.find(:all)
=> [#<Post id: 1, author_id: 1, title: "test", content: "<p>Testing ,does this really work ?</p>", created_at: "2011-03-25 15:54:06", updated_at: "2011-03-25 15:54:06">]

#log
Processing PostController#all (for 127.0.0.1 at 2011-03-26 10:12:07) [GET]
  Parameters: {"action"=>"all", "controller"=>"post"}
  User Columns (0.9ms)   SHOW FIELDS FROM `users`
  User Load (0.1ms)   SELECT * FROM `users` WHERE (`users`.`id` = 1) 
  CACHE (0.0ms)   SELECT * FROM `users` WHERE (`users`.`id` = 1) 
  CACHE (0.0ms)   SELECT * FROM `users` WHERE (`users`.`id` = 1) 
  privileges_users Columns (0.6ms)   SHOW FIELDS FROM `privileges_users`
  Privilege Load (0.1ms)   SELECT * FROM `privileges` INNER JOIN `privileges_users` ON `privileges`.id = `privileges_users`.privilege_id WHERE (`privileges_users`.user_id = 1 ) 
Rendering template within layouts/application
Rendering post/all


	


ActionView::TemplateError (You have a nil object when you didn't expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.each) on line #19 of app/views/post/all.rhtml:
16:   <div id="all_news">
17:   <ul>
18:    <% logger.debug "\n\n\t#{@post}\n\n" %>
19:   <% for posts in @post %>
20:   	<li><%= link_to posts.title, :controller=> 'post', :action=>'view',:id=>posts.id %>
21:   <%end%>
22:   </ul>

    app/views/post/all.rhtml:19:in `_run_rhtml_app47views47post47all46rhtml'
    /usr/lib/ruby/1.8/webrick/httpserver.rb:104:in `service'
    /usr/lib/ruby/1.8/webrick/httpserver.rb:65:in `run'
    /usr/lib/ruby/1.8/webrick/server.rb:173:in `start_thread'
    /usr/lib/ruby/1.8/webrick/server.rb:162:in `start'
    /usr/lib/ruby/1.8/webrick/server.rb:162:in `start_thread'
    /usr/lib/ruby/1.8/webrick/server.rb:95:in `start'
    /usr/lib/ruby/1.8/webrick/server.rb:92:in `each'
    /usr/lib/ruby/1.8/webrick/server.rb:92:in `start'
    /usr/lib/ruby/1.8/webrick/server.rb:23:in `start'
    /usr/lib/ruby/1.8/webrick/server.rb:82:in `start'

Rendered rescues/_trace (41.5ms)
Rendered rescues/_request_and_response (0.3ms)
Rendering rescues/layout (internal_server_error)
#add log detials
Processing PostController#add (for 127.0.0.1 at 2011-03-26 10:28:24) [POST]
  Parameters: {"commit"=>"► Publish Post", "action"=>"add", "authenticity_token"=>"A+JmgkBKiCxrpqk1H0n6HZJp6PnwaZFJCPjOp9N0jG0=", "controller"=>"post", "posts"=>{"title"=>"view ", "content"=>"<p>It is not working</p>"}}
  User Columns (0.9ms)   SHOW FIELDS FROM `users`
  User Load (0.2ms)   SELECT * FROM `users` WHERE (`users`.`id` = 1) 
  CACHE (0.0ms)   SELECT * FROM `users` WHERE (`users`.`id` = 1) 
  Post Columns (0.7ms)   SHOW FIELDS FROM `posts`
  CACHE (0.0ms)   SELECT * FROM `users` WHERE (`users`.`id` = 1) 
  SQL (0.1ms)   BEGIN
  Post Create (0.4ms)   INSERT INTO `posts` (`created_at`, `title`, `updated_at`, `content`, `author_id`) VALUES('2011-03-26 04:58:24', 'view ', '2011-03-26 04:58:24', '<p>It is not working</p>', 1)
  SQL (42.8ms)   COMMIT
Rendering template within layouts/application
Rendering post/add
  User Load (0.2ms)   SELECT * FROM `users` WHERE (`users`.`id` = 1) 
  Reminder Load (0.1ms)   SELECT * FROM `reminders` WHERE (recipient = '1') 
Rendered layouts/_reminder_count (5.1ms)
Completed in 112ms (View: 37, DB: 50) | 200 OK [http://localhost/post/add]

#db/migration script for this
class Post < ActiveRecord::Migration
  def self.up
  	create_table :posts do |t|
	  t.references :author
	  t.string     :title
	  t.text       :content

	  t.timestamps
	end
	create_table :post_comments do |t|
	  t.references :author
	  t.text       :comment
	  t.references :posts


	  t.timestamps	
	end
	create_table :post_tags do |t|
	  t.references :posts
	  t.references :tags
	  t.timestamps
	end
	create_table :post_views do |t|
	  t.references :posts
	  t.integer    :views
	  t.timestamps
	end
	create_table :post_ratings do |t|
	  t.references :posts
	  t.references :author
	  t.integer	   :ratings
	  t.timestamps
	end
	create_table :post_likes do |t|
	  t.references :posts
	  t.references :author
	  t.integer    :likes
	  t.integer    :dislikes
	  t.timestamps
	end
  end

  def self.down
  	drop_table :posts
	drop_table :post_comments
	drop_table :post_tags
	drop_table :post_views
	drop_table :post_ratings
	drop_table :post_likes
  end
end