Welcome to MobileRead
The User Guide is a PDF file. If you can you see all 139 pages, then the problem most likely has something to do with the e-book files that you loaded onto your reader. How did you transfer the PDF files to your reader?
Does the problem persist when you:
Change the magnification level?
HOME -> open a book -> (X) magnification -> XS|S|M|L|XL|XXL
Change the screen orientation?
HOME -> OPTIONS -> Orientation
or to change the direction
HOME -> Settings -> General Settings -> Screen Orientation
Change the page mode?
HOME -> open a book -> (X) magnification -> Page Mode
Delete and reload one of the e-books? HOME -> open a book -> OPTIONS -> Delete Book
Whenever you make any of the changes listed above, is it consistently the same page that's missing?