Weird "Unknown action" error

Hi,

When I visit this URL in my app, http://mydomain.com/admin/user/search,
I get

Unknown action
No action responded to user

I am confused by this because I have these files

app/controllers/admin_controller.rb
app/controllers/admin/user_controller.rb
app/views/admin/user/search.rhtml

Here is the code for the controllers

=====================Begin admin_controller.rb===================
class AdminController < ApplicationController
        before_filter :subscriber_login_required # defined in
application.rb
end
=====================End admin_controller.rb ====================

=====================Begin user_controller.rb====================
class Admin::UserController < ApplicationController

        def search
        end

        def searchresults
                @users = User.search(params)
        end

        def userdetails
        end
end
=====================End user_controller.rb=====================

Your help is always appreciated, - Dave

If it helps, here's my config/routes.rb file:
====================Begin routes.rb file=========================
ActionController::Routing::Routes.draw do |map|

  map.connect '', :controller => "register", :action => "start"

  map.resources :users
  map.resources :sessions
  map.signup '/signup', :controller => 'users', :action => 'new'
  map.login '/login', :controller => 'sessions', :action => 'new'
  map.logout '/logout', :controller => 'sessions', :action =>
'destroy'

  # The priority is based upon order of creation: first created ->
highest priority.

  # Sample of regular route:
  # map.connect 'products/:id', :controller => 'catalog', :action =>
'view'
  # Keep in mind you can assign values other than :controller
and :action

  # Sample of named route:
  # map.purchase 'products/:id/purchase', :controller =>
'catalog', :action => 'purchase'
  # This route can be invoked with purchase_url(:id => product.id)

  # You can have the root of your site routed by hooking up ''
  # -- just remember to delete public/index.html.
  # map.connect '', :controller => "welcome"

  # Allow downloading Web Service WSDL as a file with an extension
  # instead of a file named 'wsdl'
  map.connect ':controller/service.wsdl', :action => 'wsdl'

  # Install the default route as the lowest priority.
  map.connect ':controller/:action/:id.:format'
  map.connect ':controller/:action/:id'
end
=====================End routes.rb file=============================

Dave,

For the structure you're showing I believe that you want to use the
new 'namespace' option for route mapping:

map.namespace :admin do |adm|
  adm.resources :users
end

Here's the online API for ref:
http://api.rubyonrails.org/classes/ActionController/Routing/RouteSet/Mapper.html#M000351

AndyV