[Plone2.5] AttributeError: 'module' object has no attribute '__ac_permissions__' with "zopectl run"

We have a new customer with a very old Plone 2.5 system and we are trying to get the data out of it.
The ZEO cluster installation seems to be a bit broken Running bin/zopectl run somescript.py fails with this error. Anyone with a quick idea or hint for getting this fixed?

  File "/opt/Plone-2.5.2/lib/python/ZConfig/schema.py", line 194, in get_datatype
    return self._registry.get(dtname)
  File "/opt/Plone-2.5.2/lib/python/ZConfig/datatypes.py", line 398, in get
    t = self.search(name)
  File "/opt/Plone-2.5.2/lib/python/ZConfig/datatypes.py", line 423, in search
    package = __import__(n, g, g, component)
  File "/opt/Plone-2.5.2/lib/python/Zope2/Startup/datatypes.py", line 21, in ?
    import OFS.Uninstalled
  File "/opt/Plone-2.5.2/lib/python/OFS/Uninstalled.py", line 20, in ?
    import SimpleItem, Globals, Acquisition
  File "/opt/Plone-2.5.2/lib/python/OFS/SimpleItem.py", line 26, in ?
    import AccessControl.Role, AccessControl.Owned, App.Common
  File "/opt/Plone-2.5.2/lib/python/AccessControl/Role.py", line 21, in ?
    import Globals, ExtensionClass, PermissionMapping, Products
  File "/opt/Plone-2.5.2/lib/python/AccessControl/PermissionMapping.py", line 29, in ?
    from Owned import UnownableOwner
  File "/opt/Plone-2.5.2/lib/python/AccessControl/Owned.py", line 273, in ?
  File "/opt/Plone-2.5.2/lib/python/App/class_init.py", line 69, in default__class_init__
  File "/opt/Plone-2.5.2/lib/python/AccessControl/Permission.py", line 132, in registerPermissions
AttributeError: 'module' object has no attribute '__ac_permissions__'