I'm using double drop-down lists all throughout my application. I'm not really all that familiar with C# but in VB
syntax I have to add the 'Handles' syntax for it to fire off and fill the second drop-down otherwise changing the selectedindex change for the first drop-down does nothing. I don't know if the syntax for C# is the same but I'm guessing there might be some kind of similar functionality. Also when declaring the variables they must be declared using WithEvents.
Private Sub ddlAreaID_SelectedIndexChanged(ByVal sender As Object, ByVal e As EventArgs) Handles ddlAreaID.SelectedIndexChanged