We've created this Forum Thread with some workarounds and advice to assist you in publishing you ebook.
Epub errors: Unresolved external XML entity & Unable to locate element in toc.ncx
I uploaded epub file created with sigil that passed validation http://validator.idpf.org/ . Lulu gives me two types of errors:
IOException: Unresolved external XML entity: 'http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd' in OEBPS/Text/Section0012.html
They list this error only in certain sections even thought all my sections have the same line like this
<?xml version="1.0" encoding="utf-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
The second type of errors is like this:
Unable to locate element with id 'safety' in OEBPS/toc.ncx
All my headers have id like this: <h3 id="safety">GENERATOR SAFETY</h3> and the corresponding line in auto generated TOC looks like this:
<navPoint id="navPoint-13" playOrder="13">
<content src="Text/Section0003.html#safety" />
Is there anything I can change manually to fix these errors? Unfortunately, I don't have a Word file to let them convert it-- I did a lot of editing directly in sigil.