New Post: discount by category by quantity

Hi,
I am trying to set-up a promotion which will allow a customer to choose any product from within a category and apply a discount based on number of total units selected.
i.e. 1 x football top 2 x skating top would give a 3 qty discount.
the quantity breaks would be 1 -5 6-10 etc.
I have created 2 promotions in this way however when i select a product the system does not seem to apply the discount. it is fine when only 1 promotion is enabled.
Any thoughts?

thanks
Roger