I reinstalled all the Android sdk. At the end of the install I received the message:
Warning: File C:\Users\Guy\.android\repositories.cfg could not be loaded. (I remember now that I received this message the first time I installed the sdks).
Is this a problem? When I look in that folder, there is no file called repositories.cfg.
The error message "ERROR: In <declare-styleable> FontFamilyFont, unable to find attribute android:font" is no longer appearing, but I'm not sure how significant the repositories.cfg is.