Routing Error: Uninitialized constant in Rails 3

I have a file containing a helper class something like this:

app/classes/myfile.rb

Module mymodule
  class myclass
    # blah blah
  end
end

I want to use this class in a controller, so I wrote something like this:

require 'myfile'

class MyController < ApplicationController

  include mymodule  

  def index
    mymodule::myclass.new
  end

end

The route for the controller is defined like this:

  match 'mycontroller', :to => 'mycontroller#index'

Now for the strange behaviour I'm facing. It works perfectly fine on the first run after the server starts. But when I refresh the page or hit the URL again, I get the following error.

Routing Error

uninitialized constant MyController::mymodule

I cannot make out anything out of the error, nor can I understand why it does not work from the second hit onward only. What's happening?