If you're using System Center Operations Manager 2007 (SCOM) you may notice that your Windows Server 2008 DNS servers are in a chronic critical state, due to the DNS 2008 External Resolution Monitor. This monitor is in the Windows Server DNS 2000/2003/2008 Management Pack for Operations Manager 2007.
The DNS 2008 External Resolution Monitor performs an NSLOOKUP query for a host (NS) record at www.microsoft.com to verify that external resolution is functioning properly. Further details can be read here.
Assuming that DNS forwarding and name resolution is functioning properly, you can correct this false error by creating an override for the Query Type. Override the default value (ns) for the DNS Server class with the override value of A, as shown below:
This will cause the monitor to perform lookups for A records, which should succeed. If the monitor still fails, you may indeed have a DNS name resolution problem.