net-snmp on linux target is working, but fails snmp poling test

I'm trying to get my feet wet using SAM and a 30-day trial here, so please excuse the newbie question.

In trying to monitor a Centos 6.4 target machine using a SAM 5.5.0 server, I first installed net-snmp 5.5 on the target and used snmpconf to get me going.  I didn't do much config for performance, just mainly open up access.  IPTables are turned off.

I can successfully do "snmpwalk -v2c -cpublic <target ip address> system" from another (Solaris) machine.

But when I change the poling method for the target machine from "ICMP " to "SNMP and ICMP" and use the "test" button on that page, it seems to time-out and say "Test Failed".

Any log I can look through to get a bit better idea of what's failing? 

Thanks for any pointers....Lyle