I've encountered a pretty show-stopping bug in the free Kontakt 2 for GPO... there seems to be something wrong with Kontakt's interpretation of velocity, because its definition seems to have been changed to volume, while velocity itself stays at a default level of 127. In other words, changing the "velocity" of a note affects its volume, but not its velocity. On my MIDI controller, striking a timpani note yields a ffff crash, but lightly tapping it yields a faint, yet audible ffff crash. This is true also of velocity changes in my notation program, even in just clicking notes on Kontakt's electronic keyboard, so it seems that the problem lies with Kontakt or GPO (however, GPO continues to function normally with the old built-in Kontakt Player).
I've tried adjusting pretty much every single option I could find in Kontakt; no luck. I suspect there is a problem with the installation of Kontakt/GPO, but I did install the update as instructed. (It might be worth a try to reinstall - does doing this void one's "license," though?)
Thanks; I should clarify though. I'm not using the full version of Kontakt 2, but the GPO built-in player version... this upgrade, released a few months ago. I've posted a similar thread in the Garritan forums, and haven't gotten any feedback; in fact, nobody else seems to have this bug. Hmmmm.
One thing to add: not all instruments are actually affected by this problem. Cymbals and bass drum clearly retain their unique velocity layers, but timpani and harp do not.