build process failing

I am unable to call the build method for a has_many :through relation:

class League < ActiveRecord::Base   has_many :league_admins   has_many :league_users, :through => :league_admins, :source => :user end

class User < ActiveRecord::Base   has_many :league_admins   has_many :leagues, :through => :league_admins end

# Conotroller def create     @league = current_user.leagues.build(params[:league])     if @league.save        ...     end end

# Error RuntimeError in Admin/leaguesController#create RAILS_ROOT: /Users/chris/Documents/Projects/Rails/myleague Application Trace | Framework Trace | Full Trace app/controllers/admin/leagues_controller.rb:11:in `create'

Has something changed in Rails 2.1?