There are a few reasons why you might see this error:
- You performed a clean installation of Windows 10 instead of first upgrading from your previous version of Windows. When this happens, we aren't able to register your entitlement with the activation servers because you aren't upgrading to Windows 10. To fix this, you'll need to go back to your previous version of Windows, make sure the previous version is activated, and then upgrade to Windows 10. For more info about how to go back to a previous version of Windows, see the section in Recovery options in Windows 10.
- You upgraded to Windows 10, but the activation servers were busy. If you upgraded from an activated copy of Windows 7 or Windows 8.1, your copy of Windows 10 will be automatically activated, or you can wait a while and then select Activate now. If you performed a clean installation instead of first upgrading to Windows 10, see the info on how to fix this problem in the previous item.
- You might also see this error if you're using an invalid product key. For example, you can't use a Windows 7 or Windows 8.1 product key to activate Windows 10.