[Zope] What *IS* a Duplicate Class ID and How Does One KILL IT?!?

[Ben Ocean]

I'm trying to install a product and this error is thrown:

2001-11-14T12:03:55 ERROR(200) Zope Couldn't install EMarket
Traceback (innermost last):
   File 
/apache/ZopeInstallation/Zope_software_home/lib/python/OFS/Application.py, 
line 658, in install_product
     (Object: Zope)
     (Info: EMarket)
   File 
/apache/ZopeInstallation/Zope_software_home/lib/python/App/Product.py, line 
595, in initializeProduct
     (Object: Products.EMarket)
   File 
/apache/ZopeInstallation/Zope_software_home/lib/python/OFS/ObjectManager.py, 
line 324, in _setObject
     (Object: Products)
   File 
/apache/ZopeInstallation/Zope_software_home/lib/python/OFS/ObjectManager.py, 
line 332, in manage_afterAdd
     (Object: EMarket)
   File 
/apache/ZopeInstallation/Zope_software_home/lib/python/ZClasses/ZClass.py, 
line 492, in manage_afterAdd
     (Object: basket)
   File 
/apache/ZopeInstallation/Zope_software_home/lib/python/ZClasses/ZClass.py, 
line 446, in _register
     (Object: basket)
Duplicate Class Ids

What the heck is a Duplicate Class ID? Does anyone know? Is this possible 
to fix? How?
I'd really appreciate an answer.
Thanks,
BenO