According to Feng Shui theories, when the two doors are aligned it represents the lost of energy. This is because when energy, or chi as we like to call it, enters through the front door it moves, usually, in a straight lines. So this means that the energy is out the back door as soon as it enters the front door. When there is a lack of energy, it usually translated to a lack of wealth and health. In Feng Shui, we want energy to move about the property, not exit out back.

As for a remedy, most Feng Shui Master would advise you to relocated one of the doors. However, another, more appropriate, remedy is to use a room divider and place it directly in line between the front door and back door. The room divider needs to be made of a solid material, preferably solid wood. Avoid using the rice paper shoji screen room dividers, because they are not solid enough to divert the energy. If a screen will not work for you, then you can use any other pieces of furniture, the more solid it is made the better, to help divert the energy from moving in a straight line and out the back door.

In addition, you also want to arrange your furniture, to create "speed bumps," where the path from the front and back door is not a straight path. This will slow down the energy and helps it move to other parts of the property.

Good Luck.