Free version for three weeks since 10/9. Purchasedd Pro on 10/19; still get same message when attempting to update definitions or program. What gives, Avast?
And you have tried repair and reboot?
No luck with that. Contacted Avast directly. Any further advice or should I just wait?
If Repair doesn’t fix the problem, try the following:
Clean Install of Avast:
https://goo.gl/4Ptzkf
If you need additional help with the Clean Install, watch this:
https://youtu.be/p-h3myRD51A
Thanks for posting this document link for a clean uninstall/install. I’m filing it away for future reference in case I find myself having to do this to resolve a problem. 
Since buttoni2 joined your topic, he too recently suffered the “Host unreachable” error and that was down to his firewall blocking the update executable.
In his case the firewall was the win7 one and the executable requiring internet access was the instup.exe is in the avast\setup folder.
What is your firewall (as Avast Free and Avast Pro don’t have the Avast Firewall) ?
You could check to see if the instup.exe is in the avast\setup folder is indeed allowed in your firewall.
For more information on other files also see post https://forum.avast.com/index.php?topic=222896.msg1481589#msg1481589 other posts in that topic may also help.