Register the component libraries

Server Control

<form id="Form1" name="Form1" method="post" runat="server">
	<table>
		<tr style='font-weight:bold'>
			<td>Customer</td>
			<td>Order Date</td>
			<td>Product (Qty)</td>
		</tr>
		<tr>
			<td style='vertical-align:top'>
				<DNL:DbNetCombo 
					id="customers" 
					runat="server" 
					Sql="select customerid,companyname from customers order by companyname"
					ConnectionString="samples"
					VirtualDir=".."
					>
					<LinkedCombos>
						<DNL:LinkedCombo ComboId="orders" ParameterName="customerid"></DNL:LinkedCombo>
					</LinkedCombos>
				</DNL:DbNetCombo>
			</td>
			<td style='vertical-align:top'>
				<DNL:DbNetCombo 
					id="orders" 
					runat="server" 
					Sql="select orderid,orderdate from orders where customerid = @customerid"
					DateFormat="D"
					ConnectionString="samples"
					VirtualDir=".."
					>
					<LinkedCombos>
						<DNL:LinkedCombo ComboId="products" ParameterName="orderid"></DNL:LinkedCombo>
					</LinkedCombos>
				</DNL:DbNetCombo>		
			</td>
			<td>
				<DNL:DbNetCombo 
					id="products" 
					runat="server" 
					Sql="select '', productname & ' (' & quantity & ')' from products, [order details] where products.productid = [order details].productid and orderid = @orderid"
					ConnectionString="samples"
					VirtualDir=".."
					Size=5
					>
				</DNL:DbNetCombo>		
			</td>
		</tr>
	</table>
</form>

Customer	Order Date	Product (Qty)