Why is Kontakt opening the Library in Demo Mode?

All of the libraries on Pianobook that use Kontakt require the Full Version of Kontakt. If you are using the free version (Kontakt Player), each library will be usable in demo mode for a period of 15 minutes.

You can purchase Kontakt from Native Instruments. Typically, NI offer a 50% discount in their sales that take place in the Summer and during the Thanksgiving sales period.