Why server is showing "Temporary failure in name resolution" when trying to register it on RHN/RHSM?

Issue

• Unable to register system on Red Hat Network(RHN)
• Error:

        Could not contact Red Hat Network (xmlrpc.rhn.redhat.com) 

• rhn_register command show following error:

        An error has occurred:
        Temporary failure in name resolution
        See /var/log/up2date for more information

• Errors in /var/log/up2date

        [Mon Oct  3 09:09:05 2011] up2date A socket error occurred: (-3, 'Temporary failure in name resolution'), attempt #1
        [Mon Oct  3 09:09:11 2011] up2date A socket error occurred: (-3, 'Temporary failure in name resolution'), attempt #2
        [Mon Oct  3 09:09:16 2011] up2date A socket error occurred: (-3, 'Temporary failure in name resolution'), attempt #3
        [Mon Oct  3 09:09:21 2011] up2date A socket error occurred: (-3, 'Temporary failure in name resolution'), attempt #4
        [Mon Oct  3 09:09:26 2011] up2date A socket error occurred: (-3, 'Temporary failure in name resolution'), attempt #5
        [Mon Oct  3 09:09:26 2011] up2date Error communicating with server. The message was:
        Temporary failure in name resolution

• Errors in /var/log/RHSM/rhsm.log file

[WARNING]  @certmgr.py:103 - Exception caught while running <subscription_manager.certlib.HealingLib object at 0x84e1410> update
[ERROR]  @certmgr.py:104 - (-3, 'Temporary failure in name resolution')

• subscription-manager commands show following error:

Network error, unable to connect to server.
Please see /var/log/rhsm/rhsm.log for more information.