using the weight in discount codes

My client has decided that she wants to have a sale on an entire category of products. she wants to have a coupon based on the categegory code of the product.

we are not using the weight field at all. so i thought that it would be easy if we just hijack that field for the category code - which is a number anyways.

so i have set the weight in the cart to not be calculated by the quantity.
and i set the weight in the add to product code, to house the category code that i want.
this is all working fine, as i set these values to display in the cart area, and they do display exactly as they should. IE if category on add to cart is 500, 500 shows in the view cart (just confirms its passing over as it should).

so...
now my issue is why my discount code WONT WORK.

discount name: october2009

triggers:
total number of items > 0
if session variable txtPromoCode = october2009
if today is before 11/01/2009
number of items with Weight of 504 > 0

calculation:
based on cart subtotal times .25

Any ideas on where I went wrong?