Gantt-chart not displaying in Firefox on OS X / Vista

Gantt-chart not displaying in Firefox on OS X / Vista

Having some problems when looking at reports, specifically the task graph view and milestones graph view - have tested with firefox 2.0.0.14 on Vista and OS X 1.5 and also latest Safari in OS X - when viewing REPORTS and Task Graph View it only shows a "broken image"-picture instead of the Gantt-chart - I am pretty sure I have been able to view the chart earlier, a couple of weeks ago.

Have tested on 2 separate machines, one pc and a mac.
Just tested it in Explorer 7.0.6001.18000 and same thing there, no Gantt.

Vista and OS X installations are latest version with patches/service packs.