- Using Windows Explorer, open the folder where RoboHelp has been installed on your computer. (For me, this was C:\Program Files\Adobe\Adobe RoboHelp 2015\RoboHTML.)
- Open EBooksExt\EPUB3\OEBPS\
- Open the file named _toc.ncx. (It will open automatically in Notepad.)
- Remove the following line of code from the file:
<!DOCTYPE ncx PUBLIC "-//NISO//DTD ncx 2005-1//EN" "http://www.daisy.org/z3986/2005/ncx-2005-1.dtd">
- Save and close the _toc.ncx file.
- Back in RoboHelp, generate the eBook layout.