The ARES Commander 2017 license doesn't work directly with previous ARES Commander versions anymore. You have to install ARES Commander 2017 parallel on the same computer and check out the 2017 license key every month.
E.g. You want to run also ARES Commander 2016 again, which license is already expired and you purchased already a new Annual Plan ARES Commander 2017 license:
First you add your permission key to your Graebert licensing account via the customer portal https://customer-portal.graebert.com/ under Products.
Then you install and execute ARES Commander 2017. Now you have to login with your Graebert licensing account into the startup dialog. With the login you get a valid license key for 30 days, which can also used with ARES Commander 2016 and ARES Commander 2017. Both applications have to be on the same computer. After the login you can also start ARES Commander 2016 directly.
--> This means, you have to start and login via ARES Commander 2017 once a month, before you can use previous ARES Commander version on your computer