Hello Shenoy,
Happened to see a closed thread about the same issue. I understand that you are fetching data from BW. I was wondering whether you have 0FISCAL year maintained from BW side. What is the need of calculating it in report side which is a double work and not a standard. If in case its not maintained in your data model, try to do the calculation in BEX side rather than doing it in webI side.
If its not possible, I would like to see the variable you have created . try a test variable like No of vehicles where calmonth between(APR 2011;MAR 2012) and see if you are getting correct value.
Regards,
Nikhil Joy