I just tried recreating the doc in Calibre, went back to the metadata file and changed the language from "UND" to "ENG." After that, the Calibre file opened in Mobi Reader. So it does work, obviously depending on how the file is created.
The Calibre ePub file and folder organization is different than the organization I use (which was obtained from an IDPF link). My and the Calibre versions do not fully validate, though the Calibre version has fewer errors (but the Calibre version did not recognize some of the HTML markup, either).
|