When encountering a font issue on a Mac, Mathematica may give the following error message:

Assertion '(Unknown OS Error)' failed at LikeResource.c:56

To resolve this error message, try any of the following:

  • Restart the computer and then start Mathematica with cleared preferences. This fixes the issue in most cases.
  • Using the Font Book application, verify that the fonts on your Mac are not corrupt or duplicated. Go to Applications ► Font Book ►All Fonts.Select all the fonts, control-click them, and click Validate Fonts. Font Book checks all the fonts to see if there are any issues.

    Resolve duplicated fonts by selecting All Fonts. Then in the toolbar select Edit ► Resolve Duplicated Fonts. Try removing and reinstalling any fonts that are corrupted or duplicated.

  • Try to reinstall Mathematica’s fonts. Go to the Applications folder and control-click Mathematica. Choose Show Package Contents from the menu that appears.
  • Then navigate to SystemFiles ► Fonts ► TrueType and double-click the MathematicaFonts.dfont file. This opens up one window for each font. Click the Install Font button in each window and close each window.