Playing Midi on the S550 and OTS

[ChrisH]

Hi Guys

Other strange outcome on my S550 .. if I play some midis I cannot access any OTS keys to play along using the backtrack of the midi yet others have OTS running perfectly and it uses not only variations but also changes the voice for me as I play! The midis that work for this are mainly from performers and have the song name/initials/sample rate??   so a typical would be AllMyLovingSP022K   Anyone know what the bit after the name relates to ??  Midis with just a name tend to have no variation and no voice changes ??   Another strange thing is that all the midis with this name format seem to be in the key of "C" (makes it really easy to play along)  I'm mystified at the moment!!