Custom Alarm in vCenter not reporting in vCOPs

Hi,

I have configured a custom alarm in vCenter (5.1) to alert (and send an SNMP trap) when the storage redundancy is lost, in other words, when I lose a path to a LUN.  When I trigger this by disabling the SAN port it alerts in vCenter but not in vCOPs (5.7.1).  Other default alarms do alert OK in vCOPS but it seems none of my custom alarms do (I've tried testing with others).

I'm assuming I've missed something basic here!

Any ideas? Thanks.

Bob