I have no idea which addon is causing this or how to fix it. Here's the error I'm getting whenever I open a book.
EsoUI/Ingame/CenterScreenAnnounce/CenterScreenAnnounce.lua:1500: attempt to index a nil value
EsoUI/Ingame/CenterScreenAnnounce/CenterScreenAnnounce.lua:1500: in function 'CenterScreenAnnounce:CallExpiringCallback'
EsoUI/Ingame/CenterScreenAnnounce/CenterScreenAnnounce.lua:618: in function 'ZO_CenterScreenAnnouncementLargeLine.ExpiringCallback'
[C]: in function 'PlayFromStart'
EsoUI/Ingame/CenterScreenAnnounce/CenterScreenAnnounce.lua:632: in function 'ZO_CenterScreenAnnouncementLargeLine:PlayWipeAnimation'
EsoUI/Ingame/CenterScreenAnnounce/CenterScreenAnnounce.lua:1417: in function 'setupFunction'
EsoUI/Ingame/CenterScreenAnnounce/CenterScreenAnnounce.lua:1621: in function 'CenterScreenAnnounce:DisplayMessage'
EsoUI/Ingame/CenterScreenAnnounce/CenterScreenAnnounce.lua:1325: in function 'CenterScreenAnnounce:TryDisplayingNextQueuedMessage'
EsoUI/Ingame/CenterScreenAnnounce/CenterScreenAnnounce.lua:898: in function 'OnCenterScreenAnnounceUpdate'
HALP! I think it MIGHT have something to do with Librarian, but not 100% sure cuz it isn't mentioning that.
As it got to do with center screen announces, and there are api functiosn which add them, you could install the free software Notepad++, and use the menu search->in files: Specify your live/AddOns folder and search for the string "Announce" or "csa" or "centerscreen" to find those addons which use the function.
The function did change some patches ago and this could be an addon using the old format e.g.