[Zope] Can't update properties of a custom product

[Thierry FLORAC]

  Hi,

I'm using Zope-2.6.1 with Python-2.1.3 on Debian GNU/Linux.
I've created a custom "folder based" Zope product with several custom 
properties of several types : string, date, text, selection, boolean and 
tokens.
When I try to update these properties from the common "Properties" page, I can 
read properties values but when I try to submit the form, Zope raises an 
exception : "String error: string index out of range". 

But everything is OK if I update the same properties from a custom form 
available to my site users !!

This exception is not logged to the site error log, so I can't get any 
traceback.

Thanks for any help.

  Thierry

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