First of all, check the monitoring device surely responds to SNMP by using DcDebug tool.
Next, when the device is available for SNMP, please try the following operations.
1. Step One
Select the Monitoring device from the CAPC GUI, and push the Update Metric Families button (right side) in the Polled Metric Families tab.
2. Step Two
Select the Monitoring device from the CAPC GUI, and push the Stop Polling button in the Details tab. And after a few minutes later, push the Start Polling button at the same place.