I’ve done an upgrade in my old Windows 8 Enterprise to Windows 10 Technical Preview. After this I get the annoying message asking me to activate Windows license. For me, everything should be allright, however the Product Key in my SO is my Windows 8’s one, so it is impossible to activate it in Windows 10.
The funny thing is that if you use the MSDN to access your Product Keys, when you access the Windows 10 detail, you will see that it has no Product Key associated.
That if, even though the message says “No product key is required” is placed in the “Details” section of the product.
Now you know, use this Product Key and ready, Windows 10 is activated…