has_many :through => has_many

Thanks for your help Colin, resolved the issued by changing my model
associations....

class NameAlias < ActiveRecord::Base
  has_many :sub_tasks
  has_many :work_orders, :through => :sub_tasks

class SubTask < ActiveRecord::Base
  belongs_to :name_alias
  belongs_to :work_order

class WorkOrder < ActiveRecord::Base
  has_many :sub_tasks
  has_many :name_aliases, :through => :sub_tasks