The Only way I got SNMP OIDs to work as to do a SNMPwalk on the device using the tools menu. Once I found the OID I needed did a right click and selected add as Data Source.
If done this way the data is collected and then can be placed in a chart
I am having this same problem. Even when I find the oid with snmpwalk and create a data source. When I test the oid it returns a value of 0 even when the snmpwalk shows a real value of 30 (rssi). Is this a config problem? I am trying to graph RSSI from a deliberant 2300. this is the oid: 1.3.6.1.4.1.99.5.101.1