This is the content opf file. Is there anything in it that looks like it could be an error?
<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<package xmlns="http://www.idpf.org/2007/opf" unique-identifier="BookId" version="2.0">
<metadata xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns
pf="http://www.idpf.org/2007/opf">
<dc:identifier id="BookId" opf:scheme="UUID">urn:uuid:b8b0b36f-4be3-44d4-85a8-62e16129187a</dc:identifier>
<dc:title>Under the cover of darkness</dc:title>
<dc:creator opf:role="aut">Duane De Mello</dc:creator>
<dc:language>en</dc:language>
<meta content="0.4.2" name="Sigil version" />
<meta name="cover" content="COVER.jpg" />
</metadata>
<manifest>
<item href="toc.ncx" id="ncx" media-type="application/x-dtbncx+xml" />
<item href="Text/Section0001.xhtml" id="Section0001.xhtml" media-type="application/xhtml+xml" />
<item href="Images/mithra-ad2.jpg" id="mithra-ad2.jpg" media-type="image/jpeg" />
<item href="Images/your-message-ad.jpg" id="your-message-ad.jpg" media-type="image/jpeg" />
<item href="Images/COVER.jpg" id="COVER.jpg" media-type="image/jpeg" />
</manifest>
<spine toc="ncx">
<itemref idref="Section0001.xhtml" />
</spine>
</package>