ePub can't open in Pandigital Novel

[rickinnocal]

Hi, everyone. I have a Pandigital Novel, flashed to the latest available Android tablet firmware. (1.5)

The eBook reader software on this is Barnes & Nobles default one that came with it. I downloaded, to my computer, a free eBook in .rtf format, and used Calibre to convert it to an ePub. The converted file can be opened no problem in the Calibre reader on my computer. However, when I move the file to my Novel, and try to open it from the B&N bookshelf, it errors "Cannot open file". The detail it gives me for 'why?' is :

F_PKG_ARCHIVE_ERROR file:///PD_Novel/eBooks/EYE%20OF%20THE%20STORM%20-%20John%20Ringo.ePub/ E_ZIP_BAD_EOA_SIGNATURE;

Can anyone advise me what this means, and how to fix it?

Thanks,
Richard