If you moved your files after downloading:
Session Strings Pro 2 is a "Powered by Kontakt" library. It should appear in the left tab (Libraries tab), not just the Files tab. native instruments session strings pro 2 10 kontakt link
This happens if:
Native Instruments updated their library encryption between Kontakt 6 and 7. To make v1.0 work: If you moved your files after downloading: Session
Alternatively, if you have Kontakt 6 FULL (not Player), you can simply open the library via the Files tab (not the Libraries tab) by dragging the main instrument .nki file into the rack. This bypasses the "linking" requirement entirely. This happens if: