There is this quote in the tutorial you linked toPerhaps there is still some call for the tutorial but I can't really think of one. It is possible you can't enter previous version OEM keys in Windows 10 only retail - I don't know as I don't have OEM system.TipStarting in Windows 10 Insider Preview build 10565 and TH2 Build 10568:
Device activation improvements: Microsoft has received a lot of feedback from Insiders on making it easier to activate Windows 10 on devices that take advantage of the free upgrade offer to genuine Windows by using existing Windows 7, Windows 8 or Windows 8.1 product keys. If you install this build of the Windows 10 Insider Preview on a PC and it doesn’t automatically activate, you can enter the product key from a qualifying Windows 7, Windows 8 or Windows 8.1 used to activate the prior Windows version on the same device to activate Windows 10 by going to Settings > Update & security > Activation and selecting Change Product Key.
If you haven’t upgraded to Windows 10 yet and perform a clean installation, you’ll need to enter a qualifying product key for Windows 7, Windows 8.1 or Windows 10 or buy a license in order to activate Windows 10.
My windows 10 is now installed, but I am unable to activate it. I did enter my Windows 7 key during installation, but now I get the following message: That my key is being used on another machine.
The wonderful M$ support is as usual... useless. One of them told me I have to install Win7 first and then upgrade... otherwise it will not work.
Create an additional partition or use a spare hard drive to hold a temporary installation of Windows 7. Once you get Windows 7 activated on that computer, then you can use either the genuineticket.xml file method to activate Windows 10 on the same computer, or just entering the product key manually should then work.
But, yes, the only way we have found around that is to install Windows 7 and activate it on that computer - or keep calling Microsoft until you get someone on the phone willing to give you a Windows 10 product key.
I'll try the genuine ticket method. I'm installing a new win7 on a separate partition right now.
You will have to activate the Windows 7 using the phone activation line, but that is a simple recorded voice.