10g OEM. REPOSIROTY - Agent on the same machine

Hi Team,
 I m quite new to 10g n its oem.
 One of the machine is running OEM in my organization and we are seeing everything down on the same machine.
 OEM is running fine for other machines n Databases. for that machine processes we are getting "The agent of this target is unreachable.<http://dnlvnjtools:4889/em/console/monitoring/availOverview$type=oracle*_emrep$pageType=byDay$target=Management_20Services_20and_20Repository> "
Agent shows its already running on that machine.  Which parameter needs to set for resolving the problem.  Regards - Chirag

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