This library is being used by someone else. Try opening it again later

Same here after update in 9.1 version in MacosX (10.14.3 and 10.11.6).

It occurs when I drag and drop a pdf document on the Endnote icon in the Dock.

Same if I uninstall and reinstall application.

Same if I use a new empty library.

I hope that Clarivate will be responsive to correct this bug !