Rails - May 2009 - Recaptcha plugin problem

Hi all,

I am using radiant CMS and I am trying to create custom extension and
add recaptcha validation to it
but when I call
   if not verify_recaptcha(:private_key => ''aaaaaaaaaaa'')
     #add error
   end
I get: undefined method `verify_recaptcha'' for
#<Comment:0x4f4c460>

Bellow is the full code for my model class

class Comment < ActiveRecord::Base

	validates_presence_of :title, :author, :comment, :message =>
''required''

	validate :check_captcha

	def check_captcha
		if not verify_recaptcha(:private_key => ''aaaaaaaaaaa'')
			errors.add(:title, ''def error'');
		end
	end


end

Please someone help

10x in adance,
Ilian Iliev