[Zope] Problem with ZClasses and Permissions

Hi all, I created a ZClass. Automaticly, Zope has created a new Permission called "Add MyZClass". I activated this Permission for a role called "simple user". But, when a user connected has a "simple user" try to add an object from "MyZClass", he can't. Zope return an error... Is there any other Permissions that I should activate ? Do I need to change the configuration of "MyZClass" ? Thanks Frederic