It is possible to create zip files with a signature and other extra stuff. This can be used to ensure that the zip file is not defective and comes from the right source. It can be used as a form of reverse drm. The reader only reads files with the right signature. The end of central directory eocd is a part of all this. Possibly you are not allowed to produce content for the reader, since you do not know how to correctly sign it.
I don't know if the reader use these signatures like this, or if it might work with any eocd. You will have to ask the publisher of the reader. Maybe you just need another zip app?
More about eocd and zip signatures here:
http://www.pkware.com/documents/casestudies/APPNOTE.TXT