It has been said many times but I will repeat it again, avast doesn't block, but scans and alerts to infection, if that hasn't happened it isn't avast blocking.
Two issues in your particular problem, a) possibly your firewall blocking avast's web shield or b) remnants of Norton, a real pig to remove.
1. What is your firewall ?
Does it allow ashWebSv.exe internet access ?
- If it does delete the entry for it and do a manual update and reconnect to the internet, this will force the firewall to ask permission again.
2. How did you remove Norton ?
A link worth looking at, which is a program removal tool that can remove the remnants of a number of different Norton Programs:Removing your Norton program using SymNRT