paypal says cart is empty

Hi Eric,
I figured out why, I did not have the following:
<input type="hidden" name="item_name_<?php echo $winkee_Index+1; ?>" id="item_name_<?php echo $winkee_Index+1; ?>" value="<?php echo $winkee->DisplayInfo("ID") ?>" />

instead I had:
<input type="hidden" name="item_name_<?php echo $winkee_Index+1; ?>" id="item_name_<?php echo $winkee_Index+1; ?>" value="<?php echo $winkee->DisplayInfo("Name") ?>" />

I know that the hidden fields are sent to paypal. I have some questions about them:
1. If I put anything else here but ID, the order is not seen by paypal. So this is where I bound the prodid? Also where does the item_name come from?
<input type="hidden" name="item_name_<?php echo $winkee_Index+1; ?>" id="item_name_<?php echo $winkee_Index+1; ?>" value="<?php echo $winkee->DisplayInfo("ID") ?>" />
In this one I put the SKU Number, Where did the item_number come from?
<input type="hidden" name="item_number_<?php echo $winkee_Index+1; ?>" id="item_number_<?php echo $winkee_Index+1; ?>" value="<?php echo $winkee->DisplayInfo("SKU") ?>" />
In these fields I can add more, can I change "on0_ and if so if I wanted to change it to size, how would I do that
<input type="hidden" name="on0_<?php echo $winkee_Index+1; ?>" id="on0_<?php echo $winkee_Index+1; ?>" value="" />
<input type="hidden" name="os0_<?php echo $winkee_Index+1; ?>" id="os0_<?php echo $winkee_Index+1; ?>" value="" />
<input type="hidden" name="on1_<?php echo $winkee_Index+1; ?>" id="on1_<?php echo $winkee_Index+1; ?>" value="" />
<input type="hidden" name="os1_<?php echo $winkee_Index+1; ?>" id="os1_<?php echo $winkee_Index+1; ?>" value="" />

When I got through to PP, I noticed that the headings were limited, only ID, description, price and total. Is this because of the way I have my fields, or is it a paypal issue?
Thank you,
K