zlib decode fails with -5

[Paul Watson]

Traceback (most recent call last):
File "<string>", line 20, in ?
File "c:\Python24\lib\encodings\zlib_codec.py", line 43, in zlib_decode
output = zlib.decompress(input)
zlib.error: Error -5 while decompressing data

The -5 error appears to be a Z_BUF_ERROR from looking at the manual at 
http://www.zlib.net/

The original data was 50K.  It compressed to 30K.  When I try to decompress, 
this error occurs.

I have done this successfully on 150K of data, so I do not know why it would 
be a space issue.

Any ideas or suggestions?