[Zope] product permissions problem

hello all once again, I've got a DTML method in a product, which calls objectValues('Folder') to list some folders that are contained within the product itself. When I try it out inside the product, it works. When I use it as part of the constructor form, called from an other location, I get an unauthorized error. objectValues('Image') doesn't throw the error, so I think this must be to do with the 'Access contents information' permission mapping on the folder inside the product. (?!) I've tried giving the method a Manager proxy role to no avail. Any hints received with gratitude. seb.