Crystal Big Problem(編號:1730)

Truck.SDate is "Date Format"
Truck.EDate is "Text Format"
CryRptLb.SelectionFormula = "{Truck.SDate} >= '" & CDate(DTSPicker.Value) & "' "
error: A dat is required here
當用Truck.SDate會error, 但用Truck.EDate就ok
why????
Thx a lot