pickle problem

I have a small application that keeps track of different documents. At
times, in any module of the application (ModularSessionApp), this error
is raised;

Template traceback (most recent call last):

Traceback (most recent call last):
  File "/usr/lib/python2.3/site-packages/albatross/app.py", line 284, in run
    self.save_session(ctx)
  File "/usr/lib/python2.3/site-packages/albatross/app.py", line 350, in save_session
    ctx.save_session()
  File "/usr/lib/python2.3/site-packages/albatross/session.py", line 82, in save_session
    text = self.encode_session()
  File "/usr/lib/python2.3/site-packages/albatross/context.py", line 602, in encode_session
    raise ApplicationError('locals "%s": %s' % (name, e))
ApplicationError: locals "user": Can't pickle <class 'Base.User'>: it's not the same object as Base.User


Any idea what the problem is? user of type Base.User is kept in the
session. This happens sometimes and sometimes it works ok.

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