[Zope] import error

Might someone know a solution to my problem (short of recreating the entire site manually)... I have exported a ZMS (v.116g) site from a Zope 2.6.0 instance - Zope Version (Zope 2.6.0 (binary release, python 2.1, win32-x86), python 2.1.3, win32), Python Version 2.1.3 (#35, Apr 8 2002, 17:47:50) [MSC 32 bit (Intel)] - but receive the following error message when trying to import it into a Zope 2.5.1 running on Suse 8.1 Linux with the same revision of ZMS: 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 I'd be greatful for any suggestions on how to transfer the existing content. Aleksandra