problem zipping a text file with zlib

[DeepBleu]

I am using a python script and the zlib module to zip two text files into
two separate zip files.  They are zipping fine.  However, when I use winzip
to open the two zip files, one of them is opening fine.  The other one is
reporting that it is an invalid archive with two missing Bytes.  The two
text files are just two regular text files.  What are the conditions that
cause a zip file to fail due to missing bytes?
Thanks,
DeepBleu