[Zope] Installation problems with the "PluginIndexes" Product

Hello, If I use Zope 2.6.1, I can install the "PluginIndexes" Product without any problems. But with Zope 2.5.1 I get the following error Message: Zope Error Zope has encountered an error while publishing this resource. Error Type: SystemError Error Value: Failed to import class _extra from module Products.PluginIndexes.TextIndex.Vocabulary How can I install PluginIndexes with Zope 2.5.1? Thank you Serkan ______________________________________________________________________________ UNICEF bittet um Spenden für die Kinder im Irak! Hier online an UNICEF spenden: https://spenden.web.de/unicef/special/?mc=021101