KeyError when browsing Netwoks

Hi,

On our Zenoss Core 4.2.5 I get a KeyError on IPv6Networks in the UI when browsing Infrastructure -> Networks

In event.log I have this:

2015-10-27T08:24:44 INFO extdirect Direct request failed: '/zport/dmd/IPv6Networks': Network6Router.getTree ['/zport/dmd/IPv6Networks']
------
2015-10-27T08:24:44 INFO extdirect DirectRouter suppressed the following exception (Response e2986e59-1351-4c01-8dad-0fcc6b972255):
Traceback (most recent call last):
File "/opt/zenoss/Products/ZenUtils/extdirect/router.py", line 180, in _processDirectRequest
response.result = _targetfn(**data)
File "/opt/zenoss/Products/Zuul/routers/network.py", line 130, in getTree
tree = self.api.getTree(id)
File "/opt/zenoss/Products/Zuul/facades/__init__.py", line 122, in getTree
return ITreeNode(obj)
File "/opt/zenoss/lib/python/zope/component/hookable.py", line 33, in __call__
return self.__implementation(*args, **kw)
File "/opt/zenoss/lib/python/zope/component/hooks.py", line 115, in adapter_hook
return siteinfo.adapter_hook(interface, object, name, default)
File "/opt/zenoss/Products/Zuul/tree.py", line 47, in __init__
brain = ICatalogTool(ob).getBrain(ob)
File "/opt/zenoss/Products/Zuul/tree.py", line 248, in getBrain
rid = cat.uids[path]
KeyError: '/zport/dmd/IPv6Networks'

We do have some hosts with IPv6 addresses, but is it one of these that are faulty or maybe another thing

Hints to how this can be fixed

I have tried with the usual suspects (findposkeyerror, zenchkrels, zodbscan, et.al) but they have not been able to fix this :-(

Thomas