[Zope] copy/paste python product not working

[Tom Cameron]

I am building several python products.

They are all subclassed off:
Implicit,Persistent,RoleManager,Item,PropertyManager

I find that some products can be cut and pasted with no problem, and some
products return the error:

Traceback (innermost last):
  File C:\ZopeSite\lib\python\ZPublisher\Publish.py, line 223, in
publish_module
  File C:\ZopeSite\lib\python\ZPublisher\Publish.py, line 187, in publish
  File C:\ZopeSite\lib\python\Zope\__init__.py, line 221, in
zpublisher_exception_hook
    (Object: Traversable)
  File C:\ZopeSite\lib\python\ZPublisher\Publish.py, line 171, in publish
  File C:\ZopeSite\lib\python\ZPublisher\mapply.py, line 160, in mapply
    (Object: manage_pasteObjects)
  File C:\ZopeSite\lib\python\ZPublisher\Publish.py, line 112, in
call_object
    (Object: manage_pasteObjects)
  File C:\ZopeSite\lib\python\OFS\CopySupport.py, line 216, in
manage_pasteObjects
    (Object: Traversable)
  File C:\ZopeSite\lib\python\OFS\CopySupport.py, line 444, in
_verifyObjectPaste
    (Object: Traversable)
Copy Error: (see above)

I cant yet work out what the reason is. The products are all very similar,
so it is not obvious to me what the difference is.

Any hints would be appreciated

TIA
Tom