Two things to investigate:
Try opening the file on a 10.6 system and select different fonts for a few of your problem fields and see if this makes a difference. Snow Leopard encountered a lot of issues with fonts and font suitcases--something you can research here and at Apple's site.
Try running a recover of your file and check for problems. Sometimes a change in platform reveals issues with the file that were tolerated on one but not the other.
Absolute genius! I changed the fonts from Ariel to Geneva and, BANG!, everything is visible. Many, many thanks.