It was asking before because you are not linking main report parameters to sub report parameters.
DO NOT CREATE FORMULAS, create parameters in main and sub reports and link main report start date to sub report start date and main report end date to sub report end date.
It will not ask you twice, it will ask only once if you do the above.
Thanks,
Sastry
Still u can't resolve send report on sastrydsvs(at)gamil.
Thanks,
Sastry