title: Zope import: 'module' object has no attribute '_dt_reconstructor'
body: <p>When trying to import some objects from my server (debian) on another machine (mac), I get this error:</p>
  
  <pre><code>Traceback (innermost last):
    Module ZPublisher.Publish, line 126, in publish
    Module ZPublisher.mapply, line 77, in mapply
    Module ZPublisher.Publish, line 46, in call_object
    Module OFS.ObjectManager, line 620, in manage_importObject
    Module OFS.ObjectManager, line 638, in _importObjectFromFile
    Module ZODB.ExportImport, line 92, in importFile
    Module transaction._transaction, line 260, in savepoint
    Module transaction._transaction, line 257, in savepoint
    Module transaction._transaction, line 690, in __init__
    Module ZODB.Connection, line 1123, in savepoint
    Module ZODB.Connection, line 587, in _commit
    Module ZODB.ExportImport, line 176, in _importDuringCommit
  AttributeError: 'module' object has no attribute '_dt_reconstructor'
  </code></pre>
  
  <p>The Zope and Python versions are exactly the same (Zope 2.13.19 and Python 2.7.3) on both machines. Re-importing on the same machine works fine.</p>
  
  <p>I tracked down the object causing the problem, it is an instance of one of my custom classes. My problem is that I don't know where to look to fix the error.</p>
  
  <p>One of the base classes of this class uses DateTime, but that does not cause any problems with the other classes that inherit from this base class.</p>