Keith,
such error message comes if someone has a library object reserved e.g. in GDL editor. In order to be able to delete the library: sign in to a TW project using the user account kpeacock, open that particular object in GDL editor and release it.
After that you should be able to remove the BIM Server library.
I have checked the error message in v16 and for me the text shows up correctly so I think this has been fixed since then.
Marton Kiss
Chief Product Officer
GRAPHISOFT