I upgraded my windows 7 x64 partition on the dev machine that had a licensed VMProtect 2.13.5 on it, to windows 10 and now VMProtect 2.13.5 says it’s in demo mode.
I reinstalled it and even re-copied the .key file into the folder but that didn’t fix it.
I uninstalled the VMProtect on that windows 10 x64 partition and renamed the left behind VMProtect Ultimate folder to .old, checked the registry - found no VMProtect in HKLM or HKCU, so I reinstalled from the password protected zip I got with my order, dropped my .key file in there and voila! - Registered!