Hello,
I'm trying to access singleton class from different file and above error 
occurs.

# ============== vsynth.rb

require 'win32ole'
require 'singleton'

class VoiceSynth
   include Singleton

   attr_accessor :sapi

   def initialize
     @sapi = WIN32OLE.new('SAPI.SpVoice')
   end

   def say text
     @sapi.Speak text
   end
end

# =============== main.rb

require './vsynth'

VoiceSynth.instance.say "Hellooooo"

# =============== end

Everything looks fine for me, especially as I have already used other 
singleton class in this project and it worked.
What could be wrong?

Cheers,
Alex