If your current melody is a RealTrack you can force the track to midi by selecting that track and entering the RealTracks picker.
check the box labeled "force this track to midi" and then create a midi melody and or transfer it to the soloist track using the Melody Drop Down menu -> Edit Melody track

There are a few reasons that the soloist might not play. Check the songs soloist window and make sure the solo is set to play (yes) for the first chorus. Make sure there are no bar settings mutes in place for the soloist track in the first chorus.