Won't accept my Windows 7 product key

Trying to install Parallels with Windows 7. Why Window 7? Because my Windows 8 disk is upgrade only and I want to get to Windows 10. I know for a fact that my Windows 7 key is valid as I have installed it before (and subsequently uninstalled it).

Any thoughts?

 

Now I get a different error message: "To use the product key you entered, start the installation on a computer this running a genuine version of Windows." Since this is the first installation, I don't know how this is relevant.

 

Hello BLB,
Looks like this is related to the licensing policy of Microsoft. Please go through this link below to get more information on this licensing issue of you Windows 7.
http://windows.microsoft.com/en-in/windows7/windows-7-activation-error-invalid-product-key