[mrtg] Mrtg Graph shows inappropriate statistics

[junk at lexoncom.com]

I use mrtg to monitor juniper device SSG5.
When I was using the old cent os 5.1 the graph would show correct
staticstics where upload and download speeds would reflect the actual
speeds of the link, In my case it was 16M down and 1.5 up.
Now after I switched to ubuntu 12.10 (GNU/Linux 3.5.0-21-generic x86_64)
mrtg graph shows low values like 240K.  Is thie a  configuration issue or
version issue? I did run the config same way as on old cent os.

thx