Cannot resolve web addresses without turning off Smart Firewall on NIS

Suddenly and without any changes to my configuration or settings - or adding any new hard or software, I cannot resolve web site addresses without switching off Smart Firewall. This is true with both Chrome and IE.

Norton sites (and Google) can be accessed without problem but I cannot open all other sites. I have tried all the Chrome suggestions but none of these make any difference and in view of the fact that the problem is browser independent, I have come to the conclusion that it's an NIS issue - especially as turning off Smart Firewall allows the addresses to be resolved.

I don't want to keep on having to switch the firewall off - or keep it off permanently - so if anyone has any suggestions or solutions I would be delighted to know.

Thanks