Hi,
Im not sure why its not working, sorry. However, The comments from the author might help.

http://royaumedeole.fr/informatique/...-huanyang-vfd/

I just read them over again and remembered this setting that needed to be changed:

"In Mach3 under Ports & Pins -> Spindle Setup ensure Disable Spindle Relays is unchecked under « Relay Control »Restart Mach3."

If that doesn't help, the author of the plug in might be able to assist. Once it works, it really is great. Good luck!

Jay