registration of new host

I am facing below error while adding a new Host to existing server.the other host is also running a HDP instance

ERROR 2015-05-25 06:49:19,375 main.py:137 – Ambari agent machine hostname (sandbox.hortonworks.com) does not match expected ambari server hostname (sandboxslave.hortonworks.com). Aborting registration. Please check hostname, hostname -f and /etc/hosts file to confirm your hostname is setup correctly
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Connection to sandboxslave.hortonworks.com closed.

here is my hosts file :
192.168.50.64 hortonworks.sandbox.com
192.168.50.159 hortonworksslave.sandbox.com