InDesign EPUB 3.0 export to ADE: unable to open

Hi,

getting a non-specific error message when exporting from InDesign CC 2017 to ADE 4.5.5 as EPUB 3.0 on Windows 7:

My INDD has two JPGs, everything else is plain text, I have a navigable TOC style which I'm using in the export options, everything else is default in export. EPUB 2 export works, but removes my new line breaks.

Can anyone help?

Cheers,

Dan