Try this:

Make a copy of the file

Open the copy in RealBand

Then Select 'Save As' and choose a Band In Box file type (see image)

See if the Saved As version can open in BiaB.

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BIAB & RB2026 Win.(Audiophile), Windows 10 Professional & Windows 11, Sonar Platinum, Cakewalk by Bandlab, Izotope Prod.Bundle, Roland RD-1000, Synthogy Ivory, Kontakt, Focusrite 18i20, KetronSD2, NS40M Monitors, Pioneer Active Monitors