Jul 29 10:16:56 nag01-dev nagios: Error: External command failed -> PROCESS_SERVICE_CHECK_RESULT;192.168.XX.XXX;SNMP Traps;0;A linkUp trap signifies that the SNMP entity, acting in an 24067 Loopback10 softwareLoopback up / ifIndex.24067 (INTEGER32):24067 ifDescr.24067 (OCTETSTR):Loopback10 ifType.24067 (INTEGER):softwareLoopback enterprises.9.2.2.1.1.20.24067 ():up
Jul 29 10:16:56 nag01-dev nagios: External command error: Command failed
EDIT:
So it seems the Passive Service and Host checks were completely disabled in Nagios. I enabled them both, but only Passive Host checks actually enabled.
The Passive Service Checks remaind disabled.