problem with variable offset

Hi Gurus:

I have a pressing problem. Our client needs to compare actuals vs. planned data on a quarterly basis, so we have created a Fiscal Character characteristic Z_FISCQTR referencing the characteristic 0CALQUARTER. We are able to offset on Z_FISCQTR in our BW query, however I can't do the same in my BPS layout. The offsetting is not available when I select the variable. Does anyone know what the problem could be?

Thank you very much!