CHECK_NRPE: Error - Could not complete SSL handshake

To check if you have access to it at all attempt a simple telnet on the address:port, a ping or traceroute to see where it is blocking.

telnet IP port
ping IP
traceroute -p $port IP

Also check on the target server that the nrpe daemon is working properly.

netstat -at | grep nrpe

You also need to check the versions of OpenSSL installed on both servers, as I have seen this break checks on occasion with the SSL handshake!

If you are running nrpe as a service, make sure you have this line in your nrpe.cfg on the client side:

# example 192. IP, yours will probably differ
allowed_hosts=127.0.0.1,192.168.1.100 

You say that is done, however, if you are running nrpe under xinetd, make sure to edit the only_from directive in the file /etc/xinetd.d/nrpe.

Don't forget to restart the xinetd service:

service xinetd restart