ActionController::RequestForgeryProtection is included but helper methods not available for view?

I am getting following errors:

undefined method `protect_against_forgery?' for #<ActionView::Base:
0x32a571c>

Extracted source (around line #5):

2:
3: Thank you for signing up at Specool.com. Your first time login
must be from within this email to properly activate your account.
After that, you may login directly at specool.com.
4:
5: <% form_tag :controller => "user", :action=> "login" do %>
6: <h3>Login</h3>
7:
8: <label for="user_login">Login email:</label><br/>

RAILS_ROOT: /Users/jianshen/jedmin/working_copies/qa_feature_site
Application Trace | Framework Trace | Full Trace

/usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.1/lib/action_view/
helpers/form_tag_helper.rb:433:in `extra_tags_for_form'
/usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.1/lib/action_view/
helpers/form_tag_helper.rb:441:in `form_tag_html'
/usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.1/lib/action_view/
helpers/form_tag_helper.rb:447:in `form_tag_in_block'
/usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.1/lib/action_view/
helpers/form_tag_helper.rb:39:in `form_tag'
app/views/notification/signup_validation.erb:5:in
`_run_erb_47app47views47notification47signup_validation46erb'
app/controllers/user_controller.rb:26:in `signup'
/usr/local/bin/mongrel_rails:16:in `load'
/usr/local/bin/mongrel_rails:16

protect_against_forgery? is a method defined in
ActionController::RequestForgeryProtection and supposed to be made
available as helper method through
"helper_methods :protect_against_forgery?". But somehow my view is
not picking up these helpers methods.

Please help! I am stuck for several hours now trying to figure it out.

protect_against_forgery? is a method defined in
ActionController::RequestForgeryProtection and supposed to be made
available as helper method through
"helper_methods :protect_against_forgery?". But somehow my view is
not picking up these helpers methods.

Please help! I am stuck for several hours now trying to figure it out.

Do you have any plugins installed? This appears to work ok for me
locally. Your best bet is probably to start a fresh test app, and see
if you can repeat the problem there. If you can, then you can attach
it to a ticket in lighthouse and try to figure out the solution with
other contributors.

If you can't, then there's something up with your application.

Good luck.

I have following plugin installed, how any plugin could interfere with
this?
- act_as_list
- engines
- giberrish
- savage_beast
- simple_captcha
- sql_session_store
- tiny_mce
- white_list
- white_list_formatted_content
- will_paginate

Among those, all but sql_session_store, tiny_mce and white_list are
introducted after I upgrade to rails 2.1.1 and adding new features.