MRTG returning zero values

I am setting up MRTG with what looks like version –

software-id: “M3LM-EN1V”
upgradable-to: v5.x
nlevel: 4
features:

I can query the router with snmpget from the snmp box, get values.

[root@statistics-01 backbone-network]# snmpget -v2c -c xxxxx 99.99.99.1 ifHCOutOctets.1
IF-MIB::ifHCOutOctets.1 = Counter64: 567444294884567

I can see mrtg run and see the value returned in the log files. But the graphs always show zero. This same mrtg installation is tracking a number of cisco devices and motorola wireless devices with no problem.