Unit Price Showing as a Negative


I'm working on setting up a new adjustment program where it takes a discount off of a base price. Normally this is easy for me, but this time I'm having difficulty. I followed a similar setup for a program that is working correctly, but for some reason this new one is not working. When I have the discount applied to the ship to number the base price pulls in, but no discount takes place. When I have the discount set up to be taken off of the bill to the unit price becomes a negative number. The discount is being applied for a certain group of part numbers, which we created an item group for. I then set up a base price under a customer price group. The discount is then supposed to be taken off of that base price. The customer I'm testing it on is assigned to the right customer price group. I'm not sure where to go from here. Any idea why the unit price would come up as a negative? If you need additional info from me please let me know. Thanks for your help!