This message appears in 2 cases:
1) An incorrect activation key is used. Starting with the version 2.8.0, we changed the activation mechanism in order to allow students to use the editor for free on educational domains. This required some changes to the code base. Therefore, when you upgrade from an older version, please make sure you also change the license key with the new one. The key is already available in your account on the License Keys page.
2) The license key is expired. All editor licenses are perpetual and they come with 12 months of software updates. If you see this message after updating to a new editor version, please make sure that you have renewed the license and the license key you're using is the same with the one from your account.
If you have any further questions about the expiration message, just reach us via the contact page.