Are you sure the device you're testing on supports that OID?
Make sure that the Poller is set for Get Next, or Get Table. If the OID still comes back as unsupported, then the Device is not responding to the OID that you have set. The best way to see what your device responds to is to use our Toolset and perform a MIB Walk.
MIB Walk will discover and produce reports detailing which MIBs and OIDs are supported on a particular device. For more information about MIB Walk see the Toolset's Administrator's Guide on PDF page 324.
You can download the 30 Day Evaluation here: Evaluation of Engineer's Toolset
For more information about the Universal Device Poller, please see the Online Administrators Guide here: Universal Device Poller Online Guide