Comment 4 for bug 513368

So I located the place of the exception here:
http://bazaar.launchpad.net/~bzr-pqm/bzr/bzr.dev/view/head:/bzrlib/inventory.py#L1775
But still I don't really understand the meaning... Is there a way to workaround this problem? Is there something with the Repository wrong... Maybe somebody can explain me in this exception in detail. Thanks.