Administering NetIM : User management of stale network data
  
User management of stale network data
During collection on device configuration data for all active sources (CLI/SNMP/WMI) if the connection fails 15 consecutive times for a device, that device is considered stale and its device entry is made inactive. No further collection or polling attempts are made for inactive devices.
If the device still present in your network is an SNMP device, you may need to update the SNMP community string in the device entry. After you supply the correct community string, enable polling for the device. For more information, see Creating, modifying, and deleting device entries.
Stale devices remain in NetIM until you manually remove them. To remove a device (and all metrics data for that device) from NetIM, do the following:
Delete the device entry using the Device Manager (see Creating, modifying, and deleting device entries).
Metrics data for a deleted device cannot be recovered. Use care when deleting devices.