You can use the ePubcheck tool at http://validator.idpf.org to check each epub file and see if there are any errors (you can ignore warnings most of the time)
ERROR - EDITIONGUARD_ERROR PACKAGING ERROR: NO RESOURCE ID RETURNED FROM DRM SERVER.
This usually happens when there's something wrong with the epub files.

Written by Lanny Banong
Updated over a week ago
Updated over a week ago