Have you tried dragging and dropping individual instruments from BIAB to GB?

I have used GB a couple of times, though I mainly use Pro Tools and Reaper... I think the process is basically the same. Click on say Guitar in BIAB and drag it over a designated track in GB and then drop. It should default to the start of the song. You can then move it over to whatever point you fancy.

Try individual tracks first and see what happens. If it works it at least demonstrates that something is ok. It's sometimes a case of eliminating things to get a clearer picture.

Hope this of some use to you.

Kind regards

Gilmore Greene

"It is the best of all trades, to make songs, and the second best to sing them" - Hilaire Beloc