Apache graphs

Hello fellow xymoners

I have been using the apache status graphs with much success over the past while but I have noticed that some of the RRD files do not get the data added to them. Instead it is NaN. Now I have checked that the hobbit server can access the server status page and I have confirmed that the URL is correct but still no updates. Does anyone know of a way I can get the RRD channel to output debuging messages so I can see what is happening here? I have tried deleting the apache.rrd file and it was recreated (as expected) but still no updates go into it :(

Cheers

Iain