Hello @smartstartme
Thanks for posting in!
This error would mean that you have used the X theme license code in validating Cornerstone. You may have installed Cornerstone as a stand alone plugin with another WordPress theme or simply you have renamed the x folder into something else.
You cannot use the X theme license to validate Cornerstone. You will have to buy a separate license code from Code Canyon if you want to use Cornerstone with another theme.
If you have renamed the x folder to something else, please revert it back because Cornerstone will look for that folder and it will no longer ask you to validate it.
Hope this helps.