Data is not getting displayed after clicking on reload for set analysis

[#1]

Hi

I'm making use of calculation

sum({<MONTH_YEAR={">=$(=AddMonths(Max(date(MONTH_YEAR, 'MM')),-11))"}>} [TOTAL CHARGES])  for displaying total usage of products for last 12 months
in a bar chart.

When I'm reloading the data after placing this calculation , I'm not able to see any data in my charts

So every time I reload the data using the calculation sum([total charges]) in expression and save the qvw file and later replacing it with above calculation it's working fine.

Please let me know how to trouble shoot this one. becoz everytime changing the expression  is not good practice and i'm not able identify where its going wrong

Thanks in advance

[#2]

hi

try like this

create following variable

eg:

Vroll12 = date(addmonths(max(yourdatefield),-11),'DD/MM/YYYY')

Vmaxdate= date(max(yourdatefield),''DD/MM/YYYY')

Expression:

sum({<yourdatefield={">=$(Vroll12)<=(Vmaxdate)"}>} [TOTAL CHARGES]) 

hope this will help you

regards

nirmal