If the SNMP service on ESX fails to start, the file /etc/vmware/snmp.xml may contain an error.
Simply replace its contents with:
<?xml version="1.0" encoding="ISO-8859-1"?>
<config><snmpSettings><enable>true</enable><port>161</port><syscontact/><syslocation/><EnvEventSource>indications</EnvEventSource><communities>public</communities><loglevel>info</loglevel><authProtocol/><privProtocol/><largestorage>true</largestorage><engineid>00000063000000a100000000</engineid></snmpSettings></config>