MRTG graphs

Hello,

Following this page: http://hobbitmon.sourceforge.net/docs/hobbit-mrtg.html I added MRTG graph to my hobbit server, but when I look to trends page I didn't see anything. The RRD file is clearly updated but when I want to see image of the graph hobbitgraph.sh say: The image “http://hobbit/hobbit-cgi/hobbitgraph.sh?host=master&service=mrtg&graph_width=576&graph_height=120&first=1&count=1&disp=master&graph=hourly&action=view” cannot be displayed, because it contains errors.

I've search but found nothing to explain why I've this error.

Any idea ? Thanks

-- Christophe Truffier Pack-Solutions