In the Solaris 2.6 software a startup script is included in /etc/rc3.d that starts snmpdx (which uses port 161). You receive the error message because the FDDI SNMP agent is running, and it has already claimed port 161. Two solutions are:
Move the snmpdx start-up script
mv /etc/rc3.d/S76snmpdx /etc/rc3.d/s76snmpdx
Check if the FDDI can use a different port, other than 161.