This bug usually occurs when in5 detects a page element sitting outside of the page itself.
Make sure all page elements are sitting within the page, and are not hanging off the sides.
This bug can also occur when a landscape master page is associated with a portrait page, or vice verse.
in5 allows room for the maximum width of a page, so having a master page with the wrong orientation can cause extra space.
Ensure your master pages are all in the correct orientation.