OIDs missing? (No Such Device)

[KellyFromTexas]

Hi everyone.

I am trying to get some external sensor probes monitored in PRTG.  Most of my devices are working just fine (with the OID 1.3.6.1.4.1.318.1.1.10.2.3.2.1.4.1) but I'm getting No Such Device as an error for two of them.  I can see the sensor through the web interface so it is confirmed working.  When I use an SNMP tester to walk the OIDs, the entire 1.3.6.1.4.1.318.1.1.10 section does not appear.  

My working devices are Smart-UPS RT 3000 RM XLs.  The one that doesn't have the OIDs is a Smart-UPS SRT 5000.  Any ideas on what could be causing this?  Firmware update needed?

Thanks,

Kelly