Windows 7 activation fail (slui.exe) 0x80070002

I'm trying to upgrade from a unlicensed windows 7 to a purchased Windows 10 edition. Both are Home Premium editions, in the same language, so I should be able to upgrade without problem.

But n the install, windows 10 is telling me that my license is not correct and therefore, that it cannot continue. So I'm seeking to find a way to either :

• Buy a cheap Win7 key just so Win10 installer can pursue his work
• Use any other way to get around this issue so I can finally upgrade.

But in both cases I encounter a problem : I simply cannot use the "Activate Windows" from the control panel : It gives me an error dialog box with the error code

0x80070002

I also cannot start the sppsvc service because it gives me a "System Error 2".I tried multiple repair operations (sppsvc manual repair, WAT update, sfc /scannow, chckdsk) and none of them work.

Google did not help : this error code seems pretty unique, although I don't know why. How can I repair that ?