User want to select Employee id and then select working days

Question

 i send the run mode design and Source Code in attach file.please see the attach file.


from that i want to user first to select Employee Id and then Select the working Days Datetimepicker1.

in run mode suppose if user select the Net Payable Days combobox first i want to show the message  first to select Employee Id and then Select the working Days Datetimepicker1.


Employee Id  combobox(cb_id)                          Net Payable Days  textbox  Combobox1

working Days textbox Datetimepicker1