validates_uniqueness_of problem

I have an after_save callback when I save an Organisation record.

  def after_save     #create an admin user for this organisation     if>,       :first_name => "Admin",       :last_name => "User",       :logon_name => "admin",       :password => "secret_password",       :privilege_bits => 3,       :active => 1 )     end   end

The User table has "validate_uniqueness_of" which appears to create a problem.

class User < BaseServiceTable   before_validation_on_create :set_initial_password   serialize :permitted_programmes , Array

  attr_accessor :password_confirmation

  validates_presence_of :logon_name   validates_uniqueness_of :logon_name, :scope => :organisation_id ...........

Here is the sql from te dev log: SQL (0.1ms) BEGIN Organisation Exists (0.3ms) SELECT `organisations`.id FROM `organisations` WHERE (`organisations`.`logon_name` = BINARY 'abcd') LIMIT 1 Organisation Create (0.3ms) INSERT INTO `organisations` (`name`, `logon_name`, `password`, `active`) VALUES('ABcd Org', 'abcd', 'OrgPassword', 1) SQL (0.4ms) SELECT count(*) AS count_all FROM `users` WHERE (`users`.organisation_id = 12) SQL (53.2ms) ROLLBACK

Here is (top of) the stack trace: NoMethodError (You have a nil object when you didn't expect it! The error occurred while evaluating nil.columns_hash):     /usr/lib/ruby/gems/1.8/gems/activerecord-2.2.2/lib/active_record/ validations.rb:723:in `validates_uniqueness_of'     /usr/lib/ruby/gems/1.8/gems/activerecord-2.2.2/lib/active_record/ validations.rb:400     /usr/lib/ruby/gems/1.8/gems/activerecord-2.2.2/lib/active_record/ validations.rb:397:in `each'     /usr/lib/ruby/gems/1.8/gems/activerecord-2.2.2/lib/active_record/ validations.rb:397

I have had a look at the validation code and not sure what the problem is. Not sure if it is because User inherits from an abstract table?

I am tempted just to do the validation manually as I dont have time for lengthy messing around, but I just wondered if anyone had seen the same problem?

Cheers George