[Zope] no module datetime (imported in calender.py of zope2.7b3 win binary)

Hi, trying to install CMFCalender with zope 2.7.b3 on win (installed with the binary) I run into problems: lastpart of a longer traceback: File "L:\Zope\Zope-2.7.0-b3\bin\Lib\calendar.py", line 8, in ? import datetime ImportError: No module named datetime I also could not find any module or string 'datetime' in the whole installation path so I guess it's a bug. The calender.py of my zope 2.6.2 doesn't use datetime. Am I missing something? Any hints are most welcome, Elena