Skipped - Already in another Foreign Compressed Format

Before ZSPack attempts to compress a file, it checks if the file is 
already in a compressed format (i.e.  Zip, Gif etc).  Generally, very 
little or no compression can be achieved on a file that has already been 
compressed. 

You can force compression of these files using the '/Z' switch e.g. 

    zspack /z filenames