Your question was not closed.  It was migrated to another StackExchange site called ServerFault.  Here's the new link to your question:

https://serverfault.com/questions/214749/can-ping-ip-address-and-nslookup-hostname-but-cannot-ping-hostname

For future reference, questions regarding Server operating systems and enterprise-level networking are not appropriate for the SuperUser environment.  Please post such questions to ServerFault instead.  SuperUser is intended for questions about Workstation operating systems and Small Office/Home Office (SOHO) networks.