I am connected to my Yamaha 740 via Dell Laptop and USB midi cords. Every so often in playing a midi file, some of the voices are not heard...normally it is one or two..or sometimes the voices sound different...like a drum will sound like a bell. I take the same file and put it on disk and play it directly in my 740 and it is fine. Also, if I reboot my laptop, sometimes that will fix the problem for a while.

Any clues?????