Are you switching between midi files and performance or part playing? If so, you may be losing the GM reset. I no longer have my XP50 (went to using a laptop) but when I did I had similar problems. I started pressing the GM/GS reset before each song just to be safe. Also, I sometime experienced that with my Yamaha PSR2000 or Korg i3 and even off the PC into a sound module, so I think it might have something to do with sys ex messages too. I hope this helps. I really liked my XP, but sold it to buy something newer - ain't got there yet, but I'm looking at the new VR-760.

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Cass Pawlowski
Detroit, MI
PSR2000, Roland SC88
Cakewalk, Sonar, Power Tracks, BIAB