There is a known Kontakt bug that occasionally occurs with some of our Kontakt Player libraries, you may find the following symptoms:
1. The library may need to be re-added every time you launch Kontakt
2. You may be unable to activate the library with your serial number because the option to authorise doesn’t appear in the Native Instruments Service Centre.
3. The library may show as running in demo mode.
4. You may get the following error messages:
"Error while writing files to disk. Adding the library has failed."
"**** can not be activated. Please run the original installer of the library."
Please remove the library from the libraries pane, quit Kontakt and download the relevant file for your library below.
Once you have downloaded the file, please copy it to the following location on your computer, replacing the file that is already there (if there is one),
Mac - HD/Library/Application Support/Native Instruments/Service Centre
PC - C:\Program Files\Common Files\Native Instruments\Service Center
Then restart Kontakt and add the library.
This should resolve your issue, allowing you to authorise your library once you have restarted Kontakt.