[Zope] problem turning off permission acqusition

I have a file object (pdf type) which should be viewed only by a certain role. So I want to turn of the permission acquisition for anonymous users as they have view permissions in the top level folder. However when i I try to change it I get an Error error type : attribute error value: tag Can anybody shed some light on this ? Thanks sathya -- ########################## necessity is the mother of invention ##########################