ActionController::InvalidAuthenticityToken problem

Question

I read the answer from Mattyven on the title of What does this mean ? >> ActionController::InvalidAuthenticityToken

I agreed that "you could also send along a parameter named "authenticity_token" with the value of <%= form_authenticity_token %>". But question is how?

I put this into the form: <%= tag(:input, :type => "hidden", :name => request_forgery_protection_token.to_s, :value => form_authenticity_token) %>

It still doesn't work

my environment is : rails 2.3.8 ; rubygem 1.3.7; ruby 1.8.6; using InstantRails 2.0 (I upgrade rails by myself)