Quick note to any reading this (yeah, right) that the chap fixed this problem with some help.
Viewing post in Glory Days Horns by Orchestral Tools comments
It sounds like you're talking about the actual library: I think that that needs full Kontakt to work (and my sound sets support versions 5 and 6 - Sibelius can't even talk to Kontakt 7 on Windows. In modern versions of Kontakt all libraries need to be registered through Native Access.
My sound set works by copying the library to essentially pretend it's part of another library. But you'd still require a full version of Kontakt 5/6 for that to work on Sibelius Windows. Sibelius Mac can talk to Kontakt 7 through AU. So Kontakt already broke compatibility with Windows Sibelius, and I wouldn't be surprised if it broke Mac next.