After bouncing 6 vocal tracks to 1 Stereo track, I cannot get the original source tracks to unmute even after I recorded over two of them. All six mute lights stay on no matter what buttons I push or un-push. I can hear the new track recordings if I solo them, but they will not play back in MultiTrack, Mixdown etc. Tried switching machine off, then restart, but still they mute and stay mute-lit. Help!