Disklavier

Hello All,
What a great site - lots of tips for a new user like me.  Maybe you 
can help.  
I have just acquired an MX100 MKII with DSR and DCD upgrade.  I have 
downloaded several MIDI files from various sites, some of which, 
usually fairly small files, play fine.  Others will only play back one 
channel ie the right hand.  Does anyone have an explanation and cure 
for this?
Thanks.
Danielle