I am having the problem that apparently many have had with font disappearing due to the MS KB2753842 update.
I have applied the update and rebooted and still no fonts on stage in a simple movie that has only 1 static text field on it.
I have tried with many different fonts and they all don't work.
All fonts embedded.
I am working in Flash Professional, but for some reason could not pose the question to there, so I am trying here.
How are you embedding the font?
If you're using an [Embed] statement are you seting embed as CFF to false?
[Embed(source='fonts/arial.ttf', fontName="MyArialFont", mimeType="application/x-font-truetype", embedAsCFF="false")]
Haven't encountered the issue myself but you can always try embedding the font with the directive I posted above to see if CS6 fixes for you.
Either way glad you got back to progress. You're welcome and good luck!