Hi Mike,
I'm assuming the start point here is that I have my BiaB RealTrack song loaded into RB and it has created it's (empty) BB tracks and it's populated RealTracks. I go to the first track at the end of this list and generate a RealTrack of my choosing. This is great, but I have been able to do this before. Also with the creation of the Midi Supertrack, I have been able to do this before also.
Both of these operations are logical with what I had expected of RB. What I'm really not sure of is why I can't create and ordinary standard midi (Bass, Guitar etc) In the same way that I've just chosen a RealTrack or Midi Supertrack. But instead, when I try to do just this I get a warning box that this part is not available in the current style! So what? Why can't I choose a style in the same way as for the other track types. There are a lot available.

Is there a reason that this can't be done?