You will likely need to install Kontackt, and Service Center, register Kontackt on your
NI account, and try installing after a reboot.
Stalled installation may just mean a window popped up behind others,
and is waiting for input, so minimize as needed to check.
You may also need to create all the path and folders that the installer will seek.
Installing on a windows setup will help sleuth them out, since NI installers often place items
in 4 or more locations, be diligent in the search, Common Files, User folders,
various Documents folders, Application Data, Shared Content
yada yada typical windoze nonsense
If it's a third-party library, contact the author.