You may have a duplicate or corrupt/damaged font (not necessarily even the one having problems). Go to the Applications folder and run the FontBook app (located in Applications/Utilities folder) to resolve any duplicates. FontBook Help can guide you through the process. If you find any duplicates you must restart your system after resolving them. If font-related problems persist, you may have a damaged font file – FontBook won’t tell you if a font file is damaged. To isolate a damaged font, create a folder, then:
1. Move about half of the fonts there by families (and it's better to restart);
2. If the problem persists, it lies in one of the active fonts; if not, swap the fonts between the active folder and those in the isolation folder;
3. Colour the fonts in the isolation folder with green; and
4. Repeat from step 1
In this way, you'll be testing about 1/2 of the fonts, then 1/4, 1/8, 1/16, 1/32, etc., thus working through all the fonts in a few iterations. It's possible that you will still get an error after this, in which case you either have more than one corrupt font, or the problem lies elsewhere.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]