OK. Are you running BiaB as Administrator (2)?
I have just tried that, and the result is the same (download-manager does not open, but Sony's PC-companion opens instead)
So no change between running as admin or the normal way.
What happens if you run it directly from disk
I can run download-manager when going via the folder you show.
Here I also tried running it both as admin and the normal way, and it behaves the same way in both situations.
So running it directly works.
However, I now discovered another odd issue:
In the download-manager it says "Realtracks Sets 228-232" is NOT installed.
I then tried to re-install it from my previous download, the install-procedure completes with no error-messages, but when I re-open download-manager it still says it is not installed.
I then ran download-manager as admin, let it download and install "Realtracks Sets 228-232" (I did that because I thought perhaps it had been updated or changed from the version I originally downloaded in december), which seems to complete without error and ends with download-manager saying the "Realtracks Sets 228-232" is installed.
When I close and then re-open download-manager it once again says the realtracks 228-232 is not installed.
So I'm definitely having some weird issues here.
In BIAB-about it says:
Band-in-a-Box® for Windows
Version 2016 (431)
Activated.
And when I click "check for updates" it says it's up to date.
(I usually love a good mystery, just not BIAB-related ones

)