A line down a label which is not printed is caused by a pixel in the print head of the printer not working, in simple terms its like a mini bulb getting hot, the heat activates the direct thermal label paper to print black. When the "bulb" is blown there is no heat so that means it doesnt heat the label so you have no print . The only way to fix this is with a new print head. At JSB Print Solutions we offer service contracts to cover this along with Clinisys Pathway labels and Sunquest Ice label paper