Coupon subtracting odd amount! :(

Hi there, I followed your tutotials on setting up a coupon system on my ecart (including the setup of a recordset to hold coupons).

but for some reason its producing odd results:

for example:

Item cost £33 I add 3 of these to shopping cart (so total is £99)
the coupon is £10
but in my shopping basket it would display £89 for the discount
Then the grand total would be £10
This doesnt make any sense. Obviously ecart is using the maths of subtracting the coupon from the subtotal AND THEN subtracting this new figure again from the subtotal. But how if I followed your tutorial closely.

I am using product options (this was put together with the massive help from Ray). I am wondering if its anything to do with that?

Any ideas?

Chris