CAF - Problems with decimals in chart bar


i am currently implementing a portlet with a Service that Returns decimals. When i bind the results to my “Chart bar” it says “NaN” and no Chart is displayed.
However when i change the type of the chart to “pie” it displays the values perfectly.
How can i bind decimals (strings, for example 6,33) to the chart bar? Is this possible?

It works perfectly with a pie but not with a bar diagramm?

Thanks for any suggestions.