“Call HostServiceSystem.Start for object XX on vCenter Server YY failed” when starting snmpd on ESXi 5.1

SSH into the host and run these:

~ # esxcli system snmp set --communities 
~ # esxcli system snmp set --enable true

After that, make sure you have the port (161/udp) open in the firewall config and it should start up ok. (The root problem is the file /etc/vmware/snmp.xml – those commands fix it).