Insufficient Privileges for adding Files and Images (plone_workflow and intranet_workflow) in apublished folder

I am testing 开发者_JAVA百科just the intranet workflow (and the plone_workflow) and notice strange things. (plone 4 and 4.1)

In a folder in which a user can do everything locally, and the folder is published externally, the user can add pages, links, etc. But when trying to upload images and files, user receives "Insufficient Privileges".

That sounds strange to me. Why is the user allowed to add pages, links etc. but not images and files?

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Images and files do not have their own workflow, but they inherit the settings of the folder. Must be related to tthat.