Yes, please check that your field values have a numerical representation (like all QV time / date values should have).
If necessary, use a string interpretation function like Gysbert suggested.
If you do have DURATION values with a numeric representation, there might be another issue:
If the sum of your values extend 24 hours, you'll need to format your result not as time, but as interval.
Change the according setting in number tab of your chart or use
=interval(sum(DURATION))
In general, please avoid sentences like '..not seems to work.' Instead, tell us what you see and what you expect.
Regards,
Stefan
