The RAM might not be compatible with one another. It happens when the RAM is a different speed than the other RAM installed. A lot of people with Kingston and Ramexel RAM have the same problem. What happens is that one stick is faster than another, so the faster one is capped at slower speeds; showing an error. It's usually not the RAM, its the compatibility. Tell the customer to buy the same brand with RAM. It's highly recommended that you buy the same brand of RAM so you know they're compatible with one another.