It will remove the existing Product Lines in this plan. The Cost Plan "%(cost_plan)s" lacks the product. A bom already exists for cost plan "%(cost_plan)s". Product "%(product)s" already has a BOM assigned. You can not delete cost "%(cost)s" from plan "%(plan)s" because it's managed by system. The line "%(line)s" can only set plan or parent, not both options.