[Zope] dtml-calendar error on Zope 2.6.2

[ilflaminio at virgilio.it]

Hi all,
on Zope 2.6.2 (win 32) this code (works well in Zope 2.5.1) 
<dtml-calendar>
  <dtml-var date fmt="%d">
</dtml-calendar>
gives this error:

Error Type: KeyError
Error Value: mese_prec

Traceback (innermost last): 

Module ZPublisher.Publish, line 98, in publish 
Module ZPublisher.mapply, line 88, in mapply 
Module ZPublisher.Publish, line 39, in call_object 
Module OFS.DTMLMethod, line 126, in __call__ 
Module DocumentTemplate.DT_String, line 474, in __call__ 
Module Products.Calendar.CalendarTag, line 930, in render 
KeyError: mese_prec 

Can you help me?
thanks
mic