Hi Siva,
The credentials suppplied are only used at the time of the Agent deployment. Changing your password after agents are deployed does not effect anything in DPM.
If the error while communicating with the protection agent is ID 270, then help us with the details as well. Also check the event viewer of the File server which is being backed up - Application and System logs for any errors.
Also check the following - Does the DPMRA service on the File server start when we refresh the agent status from the DPM console.
Most common reasons for getting ID 270 is due to Firewall. Would recommend you to check that front too.
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