Try clearing the items and rebind it again.
In the
SelectedIndexChanged event of first
DropDownList clear the items of
DropDownList2 and rebind that. Try this:
protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
if(DropDownList2.Item.Count > 0)
DropDownList2.Items.Clear();
}
Hope it helps!
--Amit