My one year registration is about to expire. When I click on the register button, I get a window that asks for version of the program that I desire. I select the free antivirus and then a window comes up saying “retrieving information, please wait”. After a short wait, this window disappears and my registration period has not been updated.
My understanding is the program re-registers itself after a several days. 
Have you rebooted your computer ???
I have restarted my laptop several times over the last couple of days with the re-register still failing. The AV is just counting down the days until my registration expires.
If it’s the free version, the protection never stops The program will automatically renew after 10 days.
I had the same problem some weeks back with trying to renew my expiring Avast Free. I kept trying to renew (countless times) with no success. Eventually, about one week prior to the expiration date, a renewal attempt did succeed. Don’t know why it took so long, but I would advise to keep on trying to renew.