So I recently had to reload in my GPO program. I did so, did the upgrades that are on the website, etc, and now the samples are off in many of the solo strings keyswitched sounds.
For example, in my solo cello, on any keyswitch setting other than the one it loads up in, I get wierd, strange samples - ie, when i press a key i'll get a note and then on key release i'll get another completely different note that lasts for a second or so, 4 or 5 seme-tones higher. Tremelo and trills don't do what they are supposed to either, instead playing erratic notes.
in this case I would check if it is all the same whether an external keyboard is used or the internal keyboard of the Kontakt player.
If it is not the same then somehow your midi messages get messed up before hitting the player. In the case it is the same then I suppose your installation has failed and I would de-install and re-install GPO.