acts_as_versioned and migrations

does anybody knows why this error happens?

you can see a better formattation here: http://pastie.caboo.se/44416

thanks.

#model
  # Acts
  acts_as_versioned :version_column => :version do
    def self.included(base)
      base.belongs_to :category,
        :class_name => "Category",
        :foreign_key => "category_id"
      base.belongs_to :state,
        :class_name => "Articlestate",
        :foreign_key => "articlestate_id"
      base.belongs_to :author,
        :class_name => "User",
        :foreign_key => "author_id",
        :order => "login"
      base.belongs_to :revisor,
        :class_name => "User",
        :foreign_key => "revisor_id"
    end
  end
  # This is used in migrations, do not version defined columns.
  self.non_versioned_columns << 'comments_count' << 'hits'

#migration
class AddVersions < ActiveRecord::Migration
  def self.up
    Article.create_versioned_table
  end

  def self.down
    Article.drop_versioned_table
  end

end

#result
== AddVersions: reverting