[mrtg] Graphs from 1 server, but not 3 identical servers

[Stuart Marsden]

We are now running the latest released mrtg (as of today) on centos

we have 4 dns servers and are running a perl script to return the usage 
data via snmp

the mrtg cfg file has 3 graphs each with 2 values for each of the dns 
servers.

if i run snmpget against each of the dns severs i get sensible values 
(all sensible Counter32 values)
if I look in the .log files thoes numbers appear in the top row of data.

the 1st dns server set of graphs works fine, but the other 3 - all 
values in the log file  come out as zero, as does the graphs

as far as I can tell, and I have treble checked the dns severs are 
configured the same and the mrtg config is a "cut and paste" for each 
server just changing the target information

any suggestions?

thanks in  advance

Stuart