This issue can occur with any modular device like Cisco 6509 switches.
Modular devices contain modules identified in the cefcIntelliModuleIPAddr MIB.
Smarts IP is trying to discover all the modules contained on this device and creates ComposedOf relationship.
The problem is that the configuration of the switch allows Smarts IP to discover it, but the configuration for the internal modular card (like a firewall) does not. Since the SNMP Agent is not responding for these IPs, they are added to pending list with No Response from SNMP Agent error.