🚀 go-pugleaf

To elaborate on what Don said:

Windows doesn't actually look in the Fonts folder to find its fonts. 
(In fact, when you look at the fonts folder with Windows explorer 
you're NOT seeing what's physically in the folder! You're seeing an 
interpretation of a registry entry!)

Windows looks in the registry to find where the fonts are actually 
located. If CS3 or one of its components (Illustrator is a likely 
culprit) installed Myriad somewhere else, the system would look 
something like this:

ILLUSTRATOR           WINDOWS
   FOLDER           FONTS FOLDER        REGISTRY

   Myriad.otf             -              Myriad=Illustrator Folder

Then, if you CUT and PASTE, you're left with

       -                 Myriad.otf      Myriad=Illustrator Folder

So Windows can no longer find the font file.  Adobe products are 
non-standard (usually for the better!) and use their own techniques 
for finding fonts.

  - Herb