Markdown preview fails

I have installed markdown-preview-mode-20171121.2323 from MELPA (not the stable...) and this installs also markdown-mode-20180124.138 and other packages. All this to be used with my Win64 builds of Emacs master using MSYS2/MinGW64.

I tried to test this with a simple README.md file but both "M-x markdown-preview-mode" and Emacs menu/Markdown/Preview % Export/Preview (C-c C-cp) fail with

Error running timer: (user-error "markdown failed with exit code 1")


Notice, I have also installed the "markdown" package in MSYS2,

pacman -S markdown

... and 

(getenv "PATH")

prints

"C:\\msys64\\usr\\bin;C:\\msys64\\mingw64\\bin;[...]".

I tried also adding this to the init.el

(setq markdown-command "C:/msys64/usr/bin/markdown")

but same results..

Ciao,
Angelo.