[Daaf]

I would appreciate help with how to fix a particular Sigil ePub validation problem.

The validation results say about "OEBPS/Text/Introduction.xhtml":
* "This document is reachable but not present in the OPF <spine>", as well as that
* "This resource is reachable but not in present in the OPOF <manifest>".

But Introduction.xhtml does occur in both places:

<manifest>
<item href="Text/Introduction.xhtml" id="Introduction.xhtml" media-type="application/xhtml+xml" />
</manifest>

<spine toc="ncx">
<itemref idref="Introduction.xhtml" />
</spine>

I have checked the toc.ncx file, but Introduction.xhtml is correctly spelled there.

What is causing this file to show up as invalid?

Thank you.