148apps.com BestAppEver: “Stanza has redefined how everyone thinks about reading on a mobile device.”
— 2008 Best Free App
Does your TOC look like this?
<item id="ncx" href="toc.ncx" media-type="text/xml"/>
If so, the "media-type" is incorrect. It should read:
<item id="ncx" href="toc.ncx" media-type="application/x-dtbncx+xml"/>
The fact that epubcheck doesn't validate this requirement in the spec is a bug in epubcheck itself: