TOC nav.xhtml issue

have a small issue with the contents page at the back of the ebook. no errors in calibre check. all looks in order. Its on the nav.xhtml and its the line as follows for Chapter 5 entry. same issue with the others. once I fix one I can fix them all. I see its the element 'li' but what do I replace this line below with so it passes checker.

<li class="calibre13"><a href="Flow_6.xhtml" class="calibre14">Chapter 5</a></li>

when I put through the epub checker it picks up:

Error while parsing file 'element "li" not allowed here; expected the element end-tag or element "address", "blockquote", "del", "div", "dl", "h1", "h2", "h3", "h4", "h5", "h6", "hr", "ins", "noscript", "ns:svg", "ol", "p", "pre", "script", "table" or "ul" (with xmlns:ns="http://www.w3.org/2000/svg")'.