OK, NOW I'm getting it, with the gutsy debs, I generate sample data, click on Reservations, pick a type, check the box, hit "book" and get:

File "/usr/lib/python2.4/site-packages/zope/publisher/publish.py", line 133, in publish
  result = publication.callObject(request, obj)
File "/usr/lib/python2.4/site-packages/zope/app/publication/zopepublication.py", line 167, in callObject
  return mapply(ob, request.getPositionalArguments(), request)
File "/usr/lib/python2.4/site-packages/zope/publisher/publish.py", line 108, in mapply
  return debug_call(obj, args)
Extra information: <zope.app.pagetemplate.simpleviewclass.SimpleViewClass from /usr/lib/python2.4/site-packages/schooltool/app/browser/templates/cal_daily.pt object at 0xb38cbac>
File "/usr/lib/python2.4/site-packages/zope/publisher/publish.py", line 114, in debug_call
  return obj(*args)
File "/usr/lib/python2.4/site-packages/zope/app/pagetemplate/simpleviewclass.py", line 44, in __call__
  return self.index(*args, **kw)
File "/usr/lib/python2.4/site-packages/zope/app/pagetemplate/viewpagetemplatefile.py", line 83, in __call__
  return self.im_func(im_self, *args, **kw)
File "/usr/lib/python2.4/site-packages/zope/app/pagetemplate/viewpagetemplatefile.py", line 51, in __call__
  sourceAnnotations=getattr(debug_flags, 'sourceAnnotations', 0),
File "/usr/lib/python2.4/site-packages/zope/pagetemplate/pagetemplate.py", line 115, in pt_render
  strictinsert=0, sourceAnnotations=sourceAnnotations)()
Template "/usr/lib/python2.4/site-packages/schooltool/app/browser/templates/cal_daily.pt"
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 271, in __call__
  self.interpret(self.program)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 346, in interpret
  handlers[opcode](self, args)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 891, in do_useMacro
  self.interpret(macro)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 346, in interpret
  handlers[opcode](self, args)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 536, in do_optTag_tal
  self.do_optTag(stuff)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 521, in do_optTag
  return self.no_tag(start, program)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 516, in no_tag
  self.interpret(program)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 346, in interpret
  handlers[opcode](self, args)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 891, in do_useMacro
  self.interpret(macro)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 346, in interpret
  handlers[opcode](self, args)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 536, in do_optTag_tal
  self.do_optTag(stuff)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 521, in do_optTag
  return self.no_tag(start, program)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 516, in no_tag
  self.interpret(program)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 346, in interpret
  handlers[opcode](self, args)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 957, in do_defineSlot
  self.interpret(block)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 346, in interpret
  handlers[opcode](self, args)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 536, in do_optTag_tal
  self.do_optTag(stuff)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 521, in do_optTag
  return self.no_tag(start, program)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 516, in no_tag
  self.interpret(program)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 346, in interpret
  handlers[opcode](self, args)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 949, in do_defineSlot
  self.interpret(slot)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 346, in interpret
  handlers[opcode](self, args)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 536, in do_optTag_tal
  self.do_optTag(stuff)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 521, in do_optTag
  return self.no_tag(start, program)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 516, in no_tag
  self.interpret(program)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 346, in interpret
  handlers[opcode](self, args)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 891, in do_useMacro
  self.interpret(macro)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 346, in interpret
  handlers[opcode](self, args)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 536, in do_optTag_tal
  self.do_optTag(stuff)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 521, in do_optTag
  return self.no_tag(start, program)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 516, in no_tag
  self.interpret(program)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 346, in interpret
  handlers[opcode](self, args)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 534, in do_optTag_tal
  self.no_tag(stuff[-2], stuff[-1])
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 516, in no_tag
  self.interpret(program)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 346, in interpret
  handlers[opcode](self, args)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 745, in do_insertStructure_tal
  structure = self.engine.evaluateStructure(expr)
File "/usr/lib/python2.4/site-packages/zope/tales/tales.py", line 696, in evaluate
  return expression(self)
Template "/usr/lib/python2.4/site-packages/schooltool/app/browser/templates/calendar_macros.pt", line 184, column 2
  Expression: <StringExpr u'schooltool.CalendarPortlet'>
File "/usr/lib/python2.4/site-packages/zope/contentprovider/tales.py", line 80, in __call__
  return provider.render()
File "/usr/lib/python2.4/site-packages/schooltool/skin/skin.py", line 127, in render
  content = viewlet.render()
File "/usr/lib/python2.4/site-packages/zope/app/pagetemplate/simpleviewclass.py", line 44, in __call__
  return self.index(*args, **kw)
File "/usr/lib/python2.4/site-packages/zope/app/pagetemplate/viewpagetemplatefile.py", line 83, in __call__
  return self.im_func(im_self, *args, **kw)
File "/usr/lib/python2.4/site-packages/zope/app/pagetemplate/viewpagetemplatefile.py", line 51, in __call__
  sourceAnnotations=getattr(debug_flags, 'sourceAnnotations', 0),
File "/usr/lib/python2.4/site-packages/zope/pagetemplate/pagetemplate.py", line 115, in pt_render
  strictinsert=0, sourceAnnotations=sourceAnnotations)()
Template "/usr/lib/python2.4/site-packages/schooltool/app/browser/templates/portlet_tomorrow_events.pt"
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 271, in __call__
  self.interpret(self.program)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 346, in interpret
  handlers[opcode](self, args)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 536, in do_optTag_tal
  self.do_optTag(stuff)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 521, in do_optTag
  return self.no_tag(start, program)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 516, in no_tag
  self.interpret(program)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 346, in interpret
  handlers[opcode](self, args)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 855, in do_condition
  self.interpret(block)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 346, in interpret
  handlers[opcode](self, args)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 824, in do_loop_tal
  self.interpret(block)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 346, in interpret
  handlers[opcode](self, args)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 536, in do_optTag_tal
  self.do_optTag(stuff)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 521, in do_optTag
  return self.no_tag(start, program)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 516, in no_tag
  self.interpret(program)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 346, in interpret
  handlers[opcode](self, args)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 855, in do_condition
  self.interpret(block)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 346, in interpret
  handlers[opcode](self, args)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 408, in do_startTag
  rendered = attrAction(self, item)
File "/usr/lib/python2.4/site-packages/zope/tal/talinterpreter.py", line 485, in attrAction_tal
  evalue = self.engine.evaluateText(item[3])
File "/usr/lib/python2.4/site-packages/zope/tales/tales.py", line 704, in evaluateText
  text = self.evaluate(expr)
File "/usr/lib/python2.4/site-packages/zope/tales/tales.py", line 696, in evaluate
  return expression(self)
Template "/usr/lib/python2.4/site-packages/schooltool/app/browser/templates/portlet_tomorrow_events.pt", line 9, column 10
  Expression: <PathExpr standard:u'event/context/@@absolute_url'>
File "/usr/lib/python2.4/site-packages/zope/tales/expressions.py", line 217, in __call__
  return self._eval(econtext)
File "/usr/lib/python2.4/site-packages/zope/tales/expressions.py", line 211, in _eval
  return ob()
File "/usr/lib/python2.4/site-packages/zope/traversing/browser/absoluteurl.py", line 55, in __str__
  raise TypeError(_insufficientContext)

Which appears to be the same.