Chart images broken, Confluence 4.1.9

[ag4a...@gmail.com]

I have a pretty large Confluence instance running behind our corporate firewall.  I've installed the JavaMelody plugin, and it works great for about 24 hours, but after that, I can't view the graphs at the top of the JavaMelody page.  It appears that the plugin is working properly, but I just get the standard broken image link icon for the graphs.  Screenshot is attached.  

Anyone else ever seen this? Is there some configuration option I can set to fix it?  

Thanks.

[Vernat Emeric]

Hi,

I suggest to look at the server output for stack traces just after
displaying the monitoring reports.
There are probably some stack traces when the server is called to
generate the graphics.

And are there enough space on disk to store the files of the monitoring
data?

bye,
Emeric