Hello:  Each time I've uploaded my book's PDF to lulu.com, they return an error message saying, "Transparency: We detected an element that may be transparent within your file. We strongly recommend flattening or removing any transparencies in your file."  I've gone through all of my images and none are layered or have transparency. All are 100% opaque .jpg files. Are there any transparency settings that can potentially exist within the fonts? Thanks, Craig