cPickle from 2.2 to 2.1

[paul]

hi list,

I use cPickle in a small .cgi to save data. It run's fine on python 
2.2.3 (used for development) but fails on 2.1.1 (webserver) with:

   File "spyblog.py", line 543, in __init__
     self.entry = cPickle.load(open(log + self.filename, 'r+'))
SystemError: Failed to import class _reconstructor from module copy_reg


If I create the file on the webserver everything works, so apparently 
the 2.1.1 version of cPickle can't read files generated with the newer 
one. Does it mean the cPickle format is not compatible across versions?

thx
  Paul