#4 — AttributeError: UID when adding a Booking

I get this error using Booking/branches/2.5 on Plone 2.5.2 trying to create a booking, maybe I am doing something wrong?

Traceback (innermost last):
  Module ZPublisher.Publish, line 115, in publish
  Module ZPublisher.mapply, line 88, in mapply
  Module ZPublisher.Publish, line 41, in call_object
  Module Products.CMFFormController.FSControllerPageTemplate, line 90, in __call__
  Module Products.CMFFormController.BaseControllerPageTemplate, line 28, in _call
  Module Products.CMFFormController.ControllerBase, line 232, in getNext
   - __traceback_info__: ['id = booking_form', 'status = success', 'button=Add', 'errors={}', 'context=<RichDocument at acm-siggraph-traveling-art-show>', 'kwargs={}', 'next_action=None', '']
  Module Products.CMFFormController.Actions.TraverseTo, line 38, in __call__
  Module ZPublisher.mapply, line 88, in mapply
  Module ZPublisher.Publish, line 41, in call_object
  Module Products.CMFFormController.FSControllerPythonScript, line 104, in __call__
  Module Products.CMFFormController.Script, line 145, in __call__
  Module Products.CMFCore.FSPythonScript, line 108, in __call__
  Module Shared.DC.Scripts.Bindings, line 311, in __call__
  Module Shared.DC.Scripts.Bindings, line 348, in _bindAndExec
  Module Products.CMFCore.FSPythonScript, line 164, in _exec
  Module None, line 17, in addBookingScript
   - <FSControllerPythonScript at /plone-sites/siggraph.org/portal/addBookingScript used for /plone-sites/siggraph.org/portal/programs/traveling-art-show/acm-siggraph-traveling-art-show>
   - Line 17
  Module Products.Booking.BookingTool, line 71, in addBooking
  Module Products.Booking.BookingTool, line 91, in _addBooking
  Module Products.Booking.BookingTool, line 442, in invokeFactory
  Module Products.CMFCore.TypesTool, line 934, in constructContent
  Module Products.CMFCore.TypesTool, line 343, in constructInstance
  Module Products.CMFCore.TypesTool, line 574, in _constructInstance
  Module Products.Booking.content.Booking, line 6, in addBooking
  Module Products.ATContentTypes.content.base, line 226, in initializeArchetype
  Module Products.ATContentTypes.content.base, line 270, in edit
  Module Products.ATContentTypes.content.event, line 389, in update
  Module Products.Archetypes.BaseObject, line 466, in update
  Module Products.Archetypes.Schema, line 522, in updateAll
  Module Products.Archetypes.ClassGen, line 78, in generatedMutator
  Module Products.Archetypes.Field, line 1668, in set
AttributeError: UID