A couple things to try:

If you're using the Microsoft GS Synth, typically MIDI tracks will not render. This is in Options > Preferences > MIDI Driver.
Switching audio driver to WAS or MME may help - some ASIO drivers don't play nicely with rendering. This is in Options > Preferences > Audio.
It might be worth resetting BIAB to factory defaults - this is in the Options menu, the third entry from the top.

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