Hi I'd like to change the quantity in an AWS order. I've used the form below and that works fine for adding 1 item to the cart, but when I try to change it to a quantity of 2 it says there are no items in my cart. What am I doing wrong? Thanks.

					<form method="GET" action="http://www.amazon.com/gp/aws/cart/add.html" id="Quantity">
						<input type="hidden" name="AWSAccessKeyId" value="Access Key ID" />
						<input type="hidden" name="AssociateTag" value="Associate Tag" />


						<?php
							echo "<input type='hidden' name='ASIN.1' value='".$itemid."'/>";
						?>
						<input type="hidden" name="Quantity.1" value="1"/><br/>
						<input type="image" src="buynow.gif" value="Submit" alt="Submit">
					</form>