Since I installed Sibelius 4 and Finale 2007, I am unable to use the GPO Stand-alone player. I have owned GPO since its initial release. It has always been on the same system and the stand-alone app has always functioned without a problem. I am a late comer to Sibelius 4. When the Sibelius installer asked to me to move my existing GPO folder I simply had it copy it since I had the hard drive space and didn't want to break anything else. I have many issues with Finale 2007 but that will be in an other post.
Here are the performance details:
I load a sample, e.g. Steinway Piano.
It plays via the Kontakt Player virtual piano albeit with vibrato (what's up with that?)
MIDI keyboard - The Kontakt virtual keyboard mirrors the keys that are pressed on my MIDI keyboard but no sound occurs. This is a new behavior. It has always worked before.
I have used this setup for years, including GPO, and have never had any problems. Now I get no sound from my MIDI keyboard through the GPO stand-alone app.
The first idea that comes to mind is to check the MIDI output channel of your keyboard and make sure it matches the MIDI channel of the piano. The graphic keyboard will respond to data coming in on any MIDI channel but you will only hear sound if the loaded instrument is receiving that channel.
Not sure what to tell you about the vibrato on the piano. The piano isn't programmed to respond to vibrato. Are you certain that you are listening to the GPO Steinway and not some other piano sound when this happens?