Thanks for that, Tony. That's another approach, which, if it works for you, is the one to stick with, refine, and develop.
I got away from project folders; by that I mean a folder titled, say, "BiaB Projects,"
although at one time, those kinds of folders were seen all the time. Adobe Premiere, for example, was rushed to market before either format conversion or asset management was adequate. Today, it is a different story. Not long ago, if file formats didn't match exactly, you'd get an error message. Same thing for asset locations. There was none of this searching for files. The file system I use is probably not uncommon. Each song is a project. Each associated program or asset
is in that project folder. Mind you, not long ago, the editing programs took forever to reboot. Today, it's no time at all.
It is a different world; but still, the user can do his part. The issue is files dragged and dropped into Reaper being rejected. I'll be interested in hearing if moving those files to the explorer pane solved the problem.

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Biab for WIN 2020 -- Win 10 64bit -- Reaper/Audacity
Zoom R-16 -- Tascam DP-03-SD -- SoundTap -- Crescendo --