excel 2007 page numbers not all displaying

I have a worksheet with page numbers in the page headers but on some pages they do not print.

In page layout view you can see them all but some are faint.  When I print the document the faint ones do not print at all but the others do. How can I rectify this?

The numbers were created using Excel 2003 but I am now using Excel 2007.

My PC is running Windows 10.