What errors are you getting ?
Do you connect to the internet using a proxy (web accelerator, ISP, etc.) if so you would have to co-ordinate that with the web shield proxy ?
What is your firewall ?
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.
If that doesn't resolve it, try this setting:
From the avastUI, Settings, Updates, Proxy Settings, set it to Direct connection (no proxy), see image.