Why can’t my new 2008 server resolve DNS?

I have migrated my domain from a w2003 server to a W2008 server. The old server is no longer serving any roles in the domain. The old server has a different IP address than the new server.
All workstations in the network show the IP of the new server in their DNS settings.

The problem is that if I down the old server or unplug it’s network cable DNS stops working. I can still ping yahoo.com from the new server or a PC but I cannot display it’s web page. I have looked everywhere in my Sonicwall 2040 Pro which is doing the routing and the new server and cannot find any reference to the old DNS server’s IP address.

Where could the ghost of this old server be hiding that I cannot shut it down?