How to fix the "ERROR(NCX-001) - NCX identifier ... does not match OPF identifier ..." error?

When you validate a EPUB 2.0 package with EpubCheck, you may see the following error:

C:\fyicenter> java -jar epubcheck.jar Error-NCX-ID-Not-Match-2.0.epub
 
Validating using EPUB version 2.0.1 rules.
ERROR(NCX-001): Error-NCX-ID-Not-Match.epub/navigation.xml(-1,-1): 
 NCX identifier ("Hello") does not match 
 OPF identifier ("fyicenter.com.epub.hello").

Check finished with errors
Messages: 0 fatals / 1 error / 0 warnings / 0 infos

EPUBCheck completed

Download Error-NCX-ID-Not-Match-2.0.epub, and unzip it. You see the package file "package.opf" defines "fyicenter.com.epub.hello" as the EPUB package's unique identifier:

...
<package xmlns="http://www.idpf.org/2007/opf" version="2.0" 
  unique-identifier="MyID">
  <metadata xmlns:dc="http://purl.org/dc/elements/1.1/">
    <dc:title>Hello</dc:title>
    <dc:identifier id="MyID">fyicenter.com.epub.hello</dc:identifier>
    <dc:language>en-US</dc:language>
  </metadata>
...

But the navigation file (or NCX file) refers it as "Hello":

<?xml version="1.0" encoding="utf-8"?>
<!-- navigation.xml
  Copyright (c) 2018 FYIcenter.com 
-->
<ncx xmlns="http://www.daisy.org/z3986/2005/ncx/" version="2005-1">
    <head>
        <meta content="Hello" name="dtb:uid"/>
    </head>    
    <docTitle>
        <text>Hello</text>
    </docTitle>
    <navMap>
        <navPoint id="link1">
            <navLabel>
                <text>Hello</text>
            </navLabel>
            <content src="/content.xhtml"/>
        </navPoint>
    </navMap>
</ncx>

You can fix the error by changing content="Hello" to content="fyicenter.com.epub.hello".

⇒ Errors in GeographyofBliss_oneChapter.epub

⇐ ERROR(OPF-030) - unique-identifier Not Found

⇑ Common Errors in Reported by EpubCheck

⇑⇑ EPUB Tutorials