NoMethodError (undefined method `authenticate_admin_user!' for #<Admin::DashboardController

Question

We are using Ruby 2.1 with rails 3.2 and active admin 0.6.3. Our site is up and running on the front end but when trying to access the admin panel, it says:

"NoMethodError (undefined method `authenticate_admin_user!' for Admin::DashboardController" 

I've tried searching on net for solutions but none of them worked out.!

Any suggestions?

Edit : Admin user model

ActiveAdmin.register AdminUser do     
  #menu :priority => 2
  menu false



  index :title => 'Admin Users'+SiteSetting.site_title do                          
    column :email 
    column :role do |show|
      if show.role=="superadmin"
          status_tag('Super Admin', :ok)
      elsif show.role=="subadmin"
          status_tag('Sub Admin', :ok)
      elsif show.role=="customeadmin"
          status_tag('Custom Admin', :ok)
      else
          status_tag('Normal Admin', :ok)
      end
    end                      
    column 'Current Login', :current_sign_in_at        
    column 'Last Login', :last_sign_in_at           
    column 'Login count', :sign_in_count             
    #current_admin_user[:id]
    @count = AdminUser.count
   if @count == 1
      column do |show|
        links = link_to 'View', {:action => show.id.to_s}
        links += ' '
        links += link_to 'Edit', {:action => show.id.to_s+'/edit'}
        links
      end  
   else
     default_actions
   end  

  end                                 

  controller do
    def password
      render :text => 'test'
    end

     def new
           @admin_user = AdminUser.new
     end          

      def create

          @temp = params[:admin_user][:role_permission]
          if @temp ==nil

          else
            @new_per = @temp.join(',') 
            params[:admin_user][:role_permission] = @new_per 
          end

         @admin_user = AdminUser.new(params[:admin_user])
         @admin_user.save
         redirect_to(:action => 'index')
       end

       def edit
        @admin_user = AdminUser.find(params[:id])
      end        
  end

  filter :email                       

  sidebar :AdminUserRights do
      ul do
        li "Super Admin: Can Manage All Pages"
        li "Sub Admin: Can Only View And Update All Pages"
        li "Normal Admin: Can Only View All Pages"
        li "Custom Admin: Customize your admin via giving them custom rights of links"
      end
    end


    form :html => { :enctype => "multipart/form-data" } do |f|
            render "create" , :layout => 'active_admin'
        end  

end                    

I 've this code added in my application controller file.

Edit : Application Controller

 def authenticate_active_admin_user!
        authenticate_admin_user!
        unless current_admin_user.role?(:superadmin)
            flash[:alert] = "You are not authorized to access this resource!"
            redirect_to root_path
        end
  end