This may be due to:
1. Your full or trial license has expired at the end of the license period
2. The license level has changed e.g. after the end of your license period, it reverts to a restricted license so you can still open your Models.
3. You have registered previously and re-registered using the same email address. This means that your expired license is being picked up and we can reset this for you.
In any case of the above, please contact us at email@example.com and we will be able to help.