Oracle Forms

Hi ,
I need to do a query on a multi-record block form. The block(employee) has the following fields

emp_no emp_name emp_address start_date finish_date (in employee block)



The query is to find employees whose start_date is between DATE1 and DATE2
So I create 2 control items DATE1 and DATE2
My plan is after user enter DATE1 and DATE2 and click execute query button then in
key-exeqry:
go_block('EMPLOYEE');
Set_Block_Property('EMPLOYEE',DEFAULT_WHERE,'start_date between :control.date1 and :control.date2');
execute_query;

When I click enter query icon and I always get FRM-41003: "This function cannot be performed here"

Could you tell me what cause this error and how to fix it.

Also I need do the validate to make sure DATE2>DATE1. I put this validate in execute-query trigger and does the job.
Is this the right place to put this validation?

Many Thanks
Michael