I may have accidentally (?) fixed it!

Doing a bit more research, I tried dragging and dropping from Master (instead of 'Drums' or 'Guitar 1' etc) to a folder on my Desktop.

Normally, I get two consecutive 'Could Not Create Wave File' errors, but this time I only got one, after which the program seemed to freeze for about 20 seconds, during which time the title bar changed to 'Rendering RealTracks and Audio Tracks..please wait'.

After which I got the yellow notice pop-up thingee saying:
"D:/bb/DragDrop/Untitled Song_Render DragDrop_0.Wave successfully rendered".

Which is really weird, because upon further investigation...I didn't *have* a 'DragDrop' folder in D:/bb/!
In fact that folder didn't exist anywhere on my computer; even checked hidden folders and such.

The song didn't render to my desktop folder, didn't render to the DragDrop folder (which doesn't exist)...so where did it render to if it actually rendered? Very weird.

But since the program seemed to be expecting to dump something in D:/bb/DragDrop/, I made a DragDrop folder under /bb/.

And - well, everything seems to be working as expected!

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PC: Win10 Pro 64
32GB RAM + Two 250GB SSD + Two 4TB Externals
Software: BIAB 2017 / Reaper / Sonar / EZDrummer 2 /
EastWest Composer Cloud / Amplitube 4
Guitar: Gibson SG T Heritage Cherry