I know that this topic was posted fairly recently, but I have the same problem and do not seem to be able to fix it by magic as csloan did. My problem is absolutely identical to his. I have looked over all the suggestions and none work. This seems to happen every now and then. I wonder if it isn't something in the score itself since some scores play fine and others don't even though the mixer and MIDI settings are identical.

Something that I forgot to include... In the Playback and Input Devices menu when I hit the test button for MIDI Yoke 1 I get sound. Sibelius and Kontakt are obviously communicating but nothing is coming through on the score. In the mixer everything is set to the correct device and channel.

Please thoroughly describe the problem as well as your various settings in K2 and Sib. Also include your system information.

I've been playing around with this and I've discovered something very strange. MIDI Yoke 2 in Kontakt is sending to MIDI Yoke 1 in Sibelius. I changed all of the instruments in my multi to send to MIDI Yoke 2 and it is working. All of the instruments in the Sibelius mixer say MIDI Yoke 1. I've been using Kontakt for over a year and have never had this problem. My system is a Pentium IV 3.40GHz w/ 2GB RAM.