I´m in the same situation of @Joe User and @Jan W
I´ve just written a mail to @Wally Wally to send the details of my setup. Basically are these:
My Tvheadend server is running in IP: 192.168.10.12
Ports are already configured as HTSP 9982 and HTTP 9981
The User/Pass used is correctly configured since I´m using it in another device.
I´ve checked also that the IP address is reachable from my PC in my LAN.
My Tvheadend Server has this version: 4.3-1391~g852a10a34
TVH Player Beta is running Windows 10 Enterprise
Version: 1709
OS Build 16299.967
Anytime I try to Test connection I recieve the message: Cant connect to 192.168.10.12