Sorry - What does "It would only render a MIDI track (not ReaDrums)" mean?

"It" what?

More to the point -

I hadn't noticed a problem with this before.
Peter, are you saying that if a song uses RT and/or RD and I render, BiAB uses Midi files instead!?

I don't think so. I've had RT and Rd is songs before and I rendered them just fine ... other than the issue of the tracks starting at different times.