Systems Graphs not showing

I just freshly installed a new CentOS 5.3 Final server with Interworx and everything was working for a few hours but all of the sudden the graphs in the nodeworx control panel has stopped displaying. Now they are displaying as borken images. Has anyone seen this problem before?

Where should I start?

[update]

It was a font issue that was resolved with yum install dejavu-lgc-fonts.noarch

Thanks Paul for the help!