Playback on avid scorch not accurate

[Zarafa]

I downloaded my own composition into avid scorch but not all the instruments are playing back. (It is scored for 20 instruments only). I have checked all the instruments settings - all in unmuted. An additional problem is that the woodblock is being played by a flute. There are no untuned instruments in the "change instrument" setting. Some of the instruments that are playing have very distorted sounds - especially the brass instruments. Suggestions please.