[Zope] Attribute error on security tab

[aborel]

I created a class wich base classes are PortalContent,
DefaultDublinCoreImpl, PropertyManager).

I indicated a _properties and a manage_options structures as
following.

       manage_options=((
           {'label':'Properties', 'action':'manage_propertiesForm'},
           )
           + PortalContent.manage_options)

I have a problem when i click on the security tab, an error occures :

Attribute error
OFS.PropertyManager' module has no attribute '__bases__

What is this __bases__ attribute and how can i find it in the hierarchy ?

Thanks,

Andre