Discovery - Devices in the specified range are not active

Discovery - Devices in the specified range are not active

Hi All,
 
I am using a fresh install of OpManager 8 on Linux (eval) to prove the OpManager concept.
 
I can manually add in devices, which is great - however - auto discovery fails on any attempt to scan our /19 subnet either by range or CIDR. The error is:-

"Devices in the specified range are not active"
 
There are around 100 servers in the range specified with SNMP enabled.
 
Any ideas why this isnt working?

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