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I was also having the same error. Then I realised I did not change my NSC.ini (for NSClient) (if you installed nrpe to the clients then it is nrpe.conf (something like that)) file in the client.
There is a section with "allowed_hosts=". May be you wrote different IP then your nagios server.
And as it is saying check the logs. I am not sure where exactly it is but I think it should be under /var/log.
The logs are in the NSClient++ install location and called nsclient.log, in the log files it will tell you why the daemon is denying it access to information. It will most likely be as pennylane said that you need to set 'allowed_hosts' you may also need to change the 'password' field as well.