>> 1 If your digital piano is also not producing sound then the piano itself is probably the culprit.
No, the piano does produce a sound when notes are missing in Pianoteq.
>> 2 If you keep your eyes on the UM-1 and see it blinking when you play a chord but there's no sound from Pianoteq, then it's in your computer.
>> 3 In Pianoteq, if you open 'options' there's a tab that will show you midi data being transmitted. If you see midi data but hear no sound from Pianoteq, and your midi channel is correct, then I'd check the polyphony setting (if it's too low, you may be getting dropped notes).
I didn't look at the LED on the UM-1, but in Pianoteq, the notes were missing from the midi data. I set polyphony to 128 notes, but I don't think it is the issue. The missing notes occur randomly and don't seem related to the pedal, which I thought at first.
I am going to order a Yamaha Midi-USB cable and see if that fixes it. Who knows if Yamaha keyboards only work with Yamaha cables? Urg...
CG