Customer Exit Prompt Variables in BEx

Hi,

I created a BEx query and in that Query I need to have two prompt variables

1. Flag

2. Fiscal Month Date

Both are customer exit varioables ,so basically the abap code for Flag and Date is, by default the flag will be 0 which means whatever the inpurt Date value is ,the result set will be displayed for that date.

If the flag is changed to 1 by the user and the Date is 3/1/2013 then the result set is today-1 data

If the flag is changed to 2 by the user and the Date is 3/1/2013 then the result set is previous month data... and so on...

Can you please advice as how to create date prompt for this customer exit variable ?When I try to create it is giving me an error

Add a key figure to structure element 'selection 1' in structure 'Key figure'.

Please advice.

Thank you.