Problem with Playback

I'm trying to write a vocal harmony for SATB. I went through "Create new compostition from scratch" and selcted from the voices menu "Sporano", "Contralto", "Tenor", and "Bass". All of the notes register just fine on the score however only the Soprano line will work during playback. Also when placing the individual notes on any line except Soprano the notes will not sound like they normally do. I've also experienced this problem with a vocal line and piano line: only the vocal line will sound. But if I do just piano, all notes from the piano line sound including harmony.

How do I fix this so that I may hear the complete score during playback?

I'm running version 0.9.3 on Windows 7.

Thanks