After spending three hours trolling those forum posts in several places I finally found a solution!
STEP ONE: FontBook’ Validate Font tells me that LucindaGrande.dfont was damaged. (“FOND Bounding Box Table”) This is one of the absolute must have System Fonts.
STEP TWO:I downloaded Pacifist (https://www.charlessoft.com/) and used it to re-install the system fonts from the OS X install discs. This did not solve the problem.
“Pacifist 2.0.1 is a shareware application that opens Mac OS X .pkg package files, .dmg disk images, and .tar, .tgz, and .tar.gz file archives and allows you to extract individual files and folders out of them. This is useful, for instance, if an application which is installed by the operating system becomes damaged and needs to be reinstalled without the hassle of reinstalling all of Mac OS X. “
STEP THREE:At the recommendation of another forum discussion, I think at Apple, I downloaded and installed Linotype FontExplorer? X (https://www.linotype.com/fontexplorerX) It did its install thing then offered to clear the font caches – of which there were many. I said “yes” and re-started. Problem still exists.
FontExplorer? X sets a new standard for font management software. Linotype is pleased to announce the missing link to your font collection. With the new FontExplorer? X, font management, font sorting, font shopping and font discovery are simple and fun! FontExplorer? X gives computer users all the functionality they ever dreamed – easy to use with an elegant style.
STEP FOUR:Fontbook validation now shows TWO entries for LucindaGrande.dfont, one good, one damaged. I deleted the broken one.
STEP FIVE:I just tried to empty the Trash, and was unable to because LucindaGrande.dfont was in use. I restart again and empty the trash.
Problem solved. You must not only REPLACE the damaged system font, you must also delete it from FontBook, and then restart and empty the trash.