In the same screen, avast Settings, Updates, Update Parameters, set it to I only connect to the internet using dial-up, set the Proxy Settings to Direct connection (no proxy), assuming that you don't use a proxy to connect.
However, if you are getting this is happening on a manual update it sounds more like firewall blocking (even though you say it is allowed).
Does it allow avast.setup internet access ?
- If it does delete the entry for it and do a manual update, this should force the firewall to ask permission again.