If no RTs show up, double check that Options - Preferences points to the correct folder.
RB may have a slightly different description of the path (IE BB used the C\BB folder and RB used the C:\BB\Realtracks path), of course this could be E:\ or whatever ..
Or, as someone else said, maybe it is looking for another RT in that style (only).
I have not experienced this, but I usually use the 'Make all tracks regular tracks' feature.
You'll notice this changes those blue track names (BB tracks) to regular tracks (not blue) .. then I can do whatever I want to any track.

I do not work here, but the benefits are still awesome
Make your sound your own!