Graham, I am intrigued by your problem.

I wish I still had Windows 7 on my Toshiba laptop to test whether your problem also occurs on my setup, but alas, the hard drive died, so I put in a SSD running Windows 8.

As far as I know, the folder structure - the place you keep your BIAB songs - has no bearing on your problem.

I would have done the same troubleshooting steps that you tried.

The one piece of information missing is, did you install BIAB? You said you run it from the supplied PG Music hard drive (which is fine) and keep your songs on the internal drive (also fine). But did you do the install choice to put the program on the laptop's boot drive? I realize you don't need to, to just run the program, but I'm wondering if it makes the Windows file association work by doing so?

BIAB 2025 Win Audiophile. Software: Studio One 7 Pro, Swam horns, Acoustica-7, Notion 6, Song Master Pro, Win 11 Home. Hardware: Intel i9, 32 Gb; Roland Integra-7, Presonus 192 & Faderport 8, Royer 121, Adam Sub8 & Neumann 120 monitors.