[Zope] Importing from Zope 2.5.1

Hi We have a Zope 2.5.1 + CMF 1.3 + Plone1b1 Site I exported this site and wanted to import it into a Zope 2.6 + CMF 1.3 + Plone1b2 I get an error: ----- Error Type: AttributeError Error Value: getUserById ----- Does anyone know, what the problem is? Are there other ways to get my Zope 2.5.1 Site into the Zope 2.6? regards Lars