KeyError when publishing document

Dear developers

I have upgraded a site to Silva 1.0.2, exported it and reimported it on a
Zope 2.7.2/Silva 1.1 instance. Then I converted a Folder to a Publication.
Thus, I have to reopen the documents contained in the newly created
Publication.
Unfortunately, trying to publish some of these documents results in a
KeyError (see below).
The document can be edited and previewed without problems.

Any ideas?

Regards,
Benno
________________________________

Traceback (innermost last):
  Module ZPublisher.Publish, line 101, in publish
  Module ZPublisher.mapply, line 88, in mapply
  Module ZPublisher.Publish, line 39, in call_object
  Module Products.FileSystemSite.FSPythonScript, line 104, in __call__
  Module Shared.DC.Scripts.Bindings, line 306, in __call__
  Module Shared.DC.Scripts.Bindings, line 343, in _bindAndExec
  Module Products.FileSystemSite.FSPythonScript, line 160, in _exec
  Module None, line 25, in tab_status_approve
   - <FSPythonScript at
/silva/service_views/Silva/edit/VersionedContent/tab_status_approve used for
/silva/service_views/SilvaDocument/edit/VersionedContent/Document>
   - Line 25
  Module Products.Silva.Versioning, line 379, in
set_unapproved_version_publication_datetime
  Module Products.Silva.VersionedContent, line 345, in _reindex_version
  Module Products.Silva.Version, line 190, in reindex_object
  Module Products.ZCatalog.ZCatalog, line 558, in uncatalog_object
  Module Products.ZCatalog.Catalog, line 411, in uncatalogObject
  Module Products.ProxyIndex.ProxyIndex, line 160, in unindex_object
  Module Products.ZCTextIndex.ZCTextIndex, line 181, in unindex_object
  Module Products.ZCTextIndex.BaseIndex, line 176, in unindex_doc
  Module Products.ZCTextIndex.BaseIndex, line 304, in _del_wordinfo
KeyError: 323724257