Open the book with Sigil, a professional ebook editor and look for the file in question. We recommend that authors use Sigil for ebook conversion. It is free to use tool many professionals use. We have a guide on how to get started with it.
ERROR(RSC-005): EPUB/toc.ncx(14,71): Error while parsing file 'value of attribute "id" is invalid; must be an XML name without colons'.
The message means that you'll have to open the toc.ncx file within the epub and look for line 14. The lines will be marked. Here look for the tag 'id'.
Check the id: it should only contain latin letters and numbers. No spaces, no punctuation marks or colons.
For example, if you see
id="picture 1" change it to id="picture1".
And if you see
id="bd:4e:bh:35" change it to id="item1".
It does not matter what you write as an id as ids will be hidden in the code and won't display at the users screen. Don't forget to refresh the table of contents once you are done to make sure that every id points to the correct place.