That means that you are activating a newer version of World Creator that was released after your maintenance period ran out. Please remember, after purchasing World Creator you are granted to new updates and upgrades for a period of 12 months. Any new release after that period requires you to renew your maintenance plan, else you do not get access to it. You only have access to versions that were released before your purchase and within your maintenance period but not to versions that your maintance period does not cover.
If your maintenance period ran out, here is how to renew it:
Sing in to your account and go to Seats. Select the seat that is connected to your activation (check email) and click on the RENEW button (see image below).