When you change the orientation of a section of page to landscape, the header and footer of that section do not change orientation. Instead, the header and footer are at the top and bottom of the page on your screen, but when you print, they are in the left and right margins of the page, not the top and bottom. Any page numbers in the header or footer will appear sideways on the left or right of the printed page. These steps will help you move the page numbers to the appropriate spot and turn them on their side so they print correctly.
(Written instructions below)