Can nobody help me????
(the SSG are about the only series of Juniper devices we don't have so I don't exactly know)
In order to get this work you probably have to monitor both the Interface and the Unit (at least this is what is needed with Juniper/JunOS EX series switches)
this is because the error counters are on the interface, and the L2 MAC data is associated with the vlans [or unit 0 if you are not using VLAN tagging]
NPM uses certain sets of topology to poll the connection between layer 2 and layer 3. Running SNMPwalk to your juniper devices and check this link below show if your device supports the topology that NPM uses.