I am trying to create a bar chart do display the monthly evaluation (X-axis) versus month sum (Y-axis) bases on start and end date.

The main report structure is group filed base in one of the fowling two formulas
    monthAndYear: ToText({SINVOICED.INVDAT_0}, 'MMM-yy')
    yearAndMonth: ToText({SINVOICED.INVDAT_0}, 'yyyy-MM')

If I run the chart with monthAndYear it shows in alphabetical order (i.e. Apr-10, Aug-10, Feb-10), if run it with yearAndMonth is shows in the correct order

I want the X-axis to display something like Dez-09, Jan-10, Feb-10, Mar-10 etc.

Can this be achieved… Note that by X-axis is not date…
Thanks in advance