KeyError in pickle

[christof]

Hi,

I am using pickle/unpickle to let my program save its documents to
disk. While this it worked stable for a long time, one of my users now
complained, that he had a file which can't be loaded.

The traceback is:

    File "pickle.pyo", line 1374, in loads
    File "pickle.pyo", line 858, in load
KeyError: 'A'


Does anybody know this problem. How this can happen and how can I
avoid it?

Thanks,
Christof