Sven Hohage writes:

.... I'm working with external methods and folder proprties. The methods are iterating over properties and adding or deleting items. Until friday everything was fine.Now I got this error when I try to view the properties. .... Error Type: TypeError Error Value: len() of unsized object

Traceback (innermost last): .... File C:\Zope\lib\python\DocumentTemplate\DT_In.py, line 657, in renderwob (Object: getProperty(id)) <dtml-in> gets an argument (probably "getProperty(id)") that is not a sequence, it even does not support the "len" operation.

I assume that you somehow managed to assign a non-list value (maybe None or a number) to a list valued property. Dieter