Hi I have reacurring cracks forming underneath my windows from the inside. It is a modular home set on a cynder block foundation. The walls are made of panelling and not drywall. All the grooves in the panelling are filled in and sanded smooth and painted over. The cracks like I said are only forming underneath my windows. What is happening and how can I permantely fix this problem?

You might need to seal the entire window on the outside to prevent any water or moisture intrusion. Try sealing around the window on the outside totally. It sounds like a moisture problem. You should pay additional attention to the area just above the window on the outside as well and make sure that area is sealed properly as most water intrusion is from the top of windows. If you don't have gutters on your home would suggest installing them as well as this could keep more water and moisture from the walls of your home.