Wendy, the problem might be that your tracks, if I'm right, are all Real Tracks, so putting a Midi bass note taken from another style might not be possible.
A theoretical work around - Freeze and Save your current SGU, assuming you like it apart from the bad bass note that occurs. I am assuming that you will now take the wavs to your DAW or RB. Keeping everything as it is, look for a Midi style that is similar to the RT one you are using. It need not be exactly the same - just the genre and tempo should be about right. Load and run it and if it plays it right, Export the midi Bass line wav to your DAW. When you mix your piece simply clip out the bad RT bar and cut and paste in the midi one, deleting the rest of it. In the scheme of things it shouldnt be too noticeable.
I have done this in the past, again on Bass lines where I cant seem to get the RT to do as I ask it.
I hope this is of some help.
Ian

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