I have seen the error message "CHECK_NRPE: Error - Could not complete SSL handshake" several times and each time it has taken a bit of fiddling to sort. However the solution is easy! First, check that the file /etc/xinetd.d/nrpe contains a line "only_from" which lists the IP address you are connecting from, if not add your IP address and then restart xinetd with service xinetd restart. Other common fixes for this problem are described at Nagios Support - View FAQ.