DateTime doesn't work?

on a windows xp pro box...

test controller:
require "Date"

class DateController < ApplicationController
  def index
    d = DateTime.parse("2006-01-01")
  end
end

results in the error
  ArgumentError in DateController#index
  invalid date

in irb however it is fine:
irb(main):001:0> require "Date"
=> true
irb(main):002:0> DateTime.parse("2006-01-01")
=> #<DateTime: 4907473/2,0,2299161>

what's going on?

btw, this is using rails 1.1.6 and ruby 1.8.4 (2006-04-14)
[i386-mswin32]