Preview prints empty boxes instead of text in .pdf

Recently I noticed that when I try to print a .pdf file from Preview, even when all the text shows on the monitor correctly, when it prints, it prints empty boxes (outline of a box the size of the letters) where the texts should be.

When I open the same .pdf file using Acrobat and then print it, it prints out fine.

The printer has postscript capability and the fonts used is pretty standard (from the looks of it, Times or something like it).

I powercycled both the printer and the print server and no difference.

Why is this happening?

MacOS 10.6.8

MBP early 2011

printer: HP LJ 5MP vis JetDirect print server (networked on our Airport Extreme base station via ethernet)

any insight is appreciated.