[georgemk]

I don't know what to add.

As I've shown the manual is correct in that changing any spaces in the library name to underscore works.

Are you sure that there isn't anything odd about your calibre library name? Like an invisible character or something?

I also used calibre-debug -g calibreurl to launch calibre to do the search and it also worked. But unfortunately it doesn't show anything to do with the URL or the library name, so it wasn't giving me any clue if I misspelt the library name or not.