Undefined Method Errors

Hi

I'm relative new to RoR - but I'm having a problem with some model
relationships that I thought should have worked. Hope someone can
help.

The code...

MODELS:

class Delivery < ActiveRecord::Base
  belongs_to :vehicle
end

class Vehicle < ActiveRecord::Base
  has_many :deliveries

def self.find_all_active
    Vehicle.find(:all, :order => 'name', :conditions => ['is_active
= ?', true])
  end

end

CONTROLLER:
  @vehicles = Vehicle.find_all_active

VIEW:
  <%= vehicle.deliveries.length %>

The error...
undefined method `table_name' for Delivery:Class

Notes...
The problem seems to be the class method find_all_active. I tested the
equivalent calls in the console and they work fine - so why not when
the application is running?

Any comments appreciated

Thanks
Nick