[I am using Finale 25.2 on a Mac, running OS 10.10.  I use SmartMusicSoftSynth for playback, which I realize may not be the best option, but I haven't taken the time to learn how to set up and use any of the options.]

I have a piano part as part of a pretty large score (including string orchestra and harp).  I have muted everything by the piano part so I can hear it better while I'm working on it.  The piano part plays back erratically, almost as if it can't handle all the simultaneous voices (a problem I remember from earlier versions of Finale and other music software).

What am I doing wrong, and what should I do to fix it?

I am more than happy to send my score for someone else to look at!

Jamin