My job is configured to scan open tasks.
On the job homepage, I can see the "Open Tasks Trend" graph.
Below the graph, there is a "Configure" link.
When I click on the this link, I get the page "Configure the trend graph".
Four types are available. For all of them, the image is missing (see the attached screenshot).

URL of images is (values between <> are correct in the live environment):
http://<servername>/hudson/job/<jobname>/tasks/configure/<graphtype>/png

When I put the link in a browser, error message is: HTTP Status 404 - The requested resource () is not available.
No errors in the Tomcat logs