I seem to recall a problem on 64-bit platforms where 64-bit SNMP request
IDs were being rejected by libsnmp because it parsed them as 32-bit IDs,
but only if the values were large enough. In this situation, I was able to
probe the OIDs just fine using snmpget, but devmon failed to get the
responses, but only sometimes. Comparing packet captures of failures and
successes showed the problem.
A previously posted thread might be of some assistance:
http://sourceforge.net/p/devmon/mailman/message/30148661/