protect_from_forgery with db-session (Rails 2.3.2)

I try to use db-session with protect_from_forgery.

But I always get a error msg:

ActionController::InvalidAuthenticityToken.

application_controller.rb
protect_from_forgery #:secret => 'top_secret'

session_store.rb
ActionController::Base.session_store = :active_record_store

hope you can help me.

Best regards

After searching around it looks for me, like the authenticity_token of
the forum is not saved correctly by the session.

An therefore rails thinks the authenticity_token is invalid.