We are using the DNS provided by ISP. We have checked with them and they don't see any issue at their end. Also, the 2nd server is already registered which shows that DNS is responding. Not sure why only this server is not registering.
If your ISP is providing an authoritative DNS hosting service, then I'd probably ask them for help. Google 126.96.36.199 does not provide this service. If you wanted this service from google then I believe there is a free trial.