I've just downloaded and installed MuseScore, and loaded the file I was having trouble with.

Unfortunately, MuseScore fell at the first fence, with chords running at 4 beats to the bar with the melody running in 3/4 underneath, becoming ever more out-of-phase with the chords. There are also double-stops in the melody which aren't in the original.

I notice that the BIAB import feature is marked as "experimental", so I shouldn't be harsh in my criticism, but a MuseScore conversion is certainly not usable as a quick-fix for a faulty BIAB leadsheet.