Since the latest update I have been receiving the following error message when trying to access 'Book''. ''sfntread library error'' All other tabs are okay. I am running the latest edition of Windows 10 64 bit. Help/advice please. Geoff
There are a number of threads in this forum about this error message: https://forums.adobe.com/search.jspa?q=sfntread+library+error&place=%2Fplaces%2F1383621 . Unless someone has a more authoritative answer, you could try the workarounds described in those threads.
I suspect your preference file or a font may be corrupt. Best you reset same by holding the Shift and Alt keys when relaunching Lightroom.