(First a little excuse: I've got an extreme lack of time right now, otherwise I would try to isolate the problem -- but maybe it's a bug already known) There seems to be a problem calling external methods with default parameters from DTML docs. I've got an external method (original signature): def pfadleiste(self, pfadleisten_info, cut_last_entry): "..." calling it via <!--#var "pfadleiste(self, info, 0)"--> is no problem at all, but if I change the signature to def pfadleiste(self, pfadleisten_info, cut_last_entry=1): calling the same page in an identical context gives one of these darned screwed-up "TypeError: read-only buffer, class" error that unluckily hide the original exception (a permanent pain when debugging -- if this changes with the new Zope version it would be a reason for me to upgrade even my existing system). Stefan