I tried to run tex4ebook on the same MWE of this question (actually I tried also with a much more complex source, getting the same problem)
\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\begin{document}
\section{section 1}
this is a test
\end{document}
with
tex4ebook test.tex -format epub3 -shell-escape
and I got the following error:
tex4ebook:unable to convert to number: -m
I just updated with tlmgr update --self --all --reinstall-forcibly-removed my TexLive 2016 Windows distribution (which updated tex4ht among others), and htlatex works correctly on my system. For example, running
htlatex test.tex "xhtml,charset=utf-8,fn-in,3,next,mouseover" " -cunihtf -utf8"
produces the expected xhtml file.
Any clue?
--I guess you might want to fix the documentation on CTAN ( http://mirrors.ctan.org/support/tex4ebook/tex4ebook-doc.pdf ), since from that PDF seems that also the full length option version (likeformat) should be called with a single-. I guess Tex replaced the double dash with a single longer dash. – mmj Jul 31 '16 at 19:16