A family of Microsoft presentation graphics products that offer tools for creating presentations and adding graphic effects like multimedia objects and special effects with text.
How have you determined that he has the correct font loaded?
Have him open the presentation and choose the Home tab, then click the downward pointing arrowhead next to Replace and choose Replace Fonts.
Open the upper listbox; verify that there's a TT icon next to each of the fonts. Any font with a question mark icon is missing, not installed on his system and is likely to be the root of the problem.
If any fonts have printer icons next to them, that could also be a problem.