The Windows installer stops with "BookyAI cannot be closed" and then "Failed to uninstall old application files". What should I do?

The installer found a copy of BookyAI still running in the background and was not allowed to close it, so it could not replace the old files. Your books are safe: they are in your books folder and the installer never touches them. Restart your PC, do not open BookyAI, and run the installer straight away. If the message comes back, press Ctrl + Shift + Esc to open Task Manager, go to the Details tab, select every "BookyAI.exe" and click End task, then right-click the installer and choose "Run as administrator". If someone else on this PC has their own Windows account, close BookyAI there too, or sign them out. From version 1.9.22, BookyAI no longer leaves its narration or Listen processes running after it closes unexpectedly, which was one way this could happen.