Had the same issue 2 days back, I think it's the problem with their service. I'm now using Google DNS and everything is working fine for me, here http://www.pingzic.com/dns-server-unavailable/ I found few tips to resolve this issue, and setting Google public DNS worked for me.

In reply to a post by waqasahmed:

Had the same issue 2 days back, I think it's the problem with their service. I'm now using Google DNS and everything is working fine for me, here http://www.pingzic.com/dns-server-unavailable/ I found few tips to resolve this issue, and setting Google public DNS worked for me.

Wow you replied to a 2 yr old thread and revived it, Many ISP's DNS servers are unreliable or often less reliable than other public DNS servers, Personally i don't use google