Hi,
I also had that issue where the license would not "stick" and reverted back to the demo mode. This is on a brand new Lenova H50-55 PC with Win 8.1 (3 days old).
I used both Mach 4 VER 2 Builds 2651 and build 2673 - no luck.
I finally refreshed my brand new Win8.1 machine then updated to Win10.
A day later (this morning) I was finally able to get the license to stay.
I don't know what that was all about.
I ended up using Mach 4 Ver 2 build 2651 because the Warp9 website claims its the tested one to work with my Ethernet Smooth Stepper (ESS).
Next, I added the unzipped two files for the ESS plugins to the Mach 4 plugin folder. Open Mach 4, enter, when asked, the 10.9.9.9 IP address for the ESS (which worked fine on a demo Mach 3 install on an old XP computer) but Mach 4 now won't complete the "open" part by giving an error that it must close. Dead again, with no idea why.
To post this experience I used my trusty WIN 7 laptop to register on this forum and the "Gotcha" slider won't move. So I couldn't register. What?
?.....
I finally ended up registering on my new Mach4 PC and its "Gotcha" sliders work.
What a frustrating process just to get my cnc running - and it still bogged down with some unknown problem.
I have considered going Linux, but it is way too fussy regarding latency and even my brand new Lenova PC had a severe latency that it is not recommended. I had one old XP machine that did have a decent latency - but I can't use the ESS with Linux, and I would lose my Mach 4 - ESS investment too. CRAP....
Now I'm waiting for Support, or this forum to help me.