This was discussed about 2 weeks ago here at the Synthzone. You must hit function button on your Tyros, then go to Utility, then hit Midi, then go to Midi Receive tab and change the word "song" next to channel 1 to say "keyboard". You also have to make sure that your host button on the P90 it pushed over to the word "midi" and not "PC or MAC".
George Kaye
Kaye's Music Scene
Reseda, California