zms update trouble

Dear ZMS users,

im in the process of update an old ZMS site for an customer who asked 
me to do this for him.
I've already updated some own ZMS instances in the last year. From ZMS 
2.7 to the current 2.11 release and it worked just fine.

But this one is much older now and I ran in some troubles...
I've deactivated all Workflow, Cache, History, Catalog.

Start System:
Zope 2.6.4, Python 2.2.3
ZMS 2.1.2.7 (build #117b)

Step 1 System:
Zope 2.7.4, Python 2.3.4
zms_21_116m32pr.tar.gz
->Import successful

Step 2 System:
Zope 2.7.4, Python 2.3.4
ZMS-2.2.0-b28
-> Import failed


Exception traceback:

Exception Type TypeError 
Exception Value can't pickle function objects 

Traceback (innermost last): 

Module ZPublisher.Publish, line 104, in publish 
Module Zope.App.startup, line 221, in commit 
Module ZODB.Transaction, line 193, in commit 
Module ZODB.Transaction, line 233, in commit 
Module ZODB.Transaction, line 348, in _commit_objects 
Module ZODB.Connection, line 418, in commit
__traceback_info__: (('Products.zms._zmsattributecontainer', 
'ZMSAttributeContainer'), '\x00\x00\x00\x00\x00\x00D\x1e', '') 
Module copy_reg, line 69, in _reduce_ex 
TypeError: can't pickle function objects 


Any help or suggestion is much apprectiated

Best!
Frank Rossi