CUSTOM.pll is not working as expected

Dear All,

I want to make COUPONS block disable for Insert, Update and Delete when there is a coupon number exists. I am doing this using custom.pll but COUPONS block is still disable even when there is no coupon number. Further I am using custom.pll because I want to disable delete button in standard toolbar. Otherwise I would prefer to use forms personalization. Forms personalization is not able to disable delete button in standard toolbar and this results giving option user to delete coupon number. I am using EBS 12.1.3