You didn't say you were getting a red circle status indicator on the DnD. My assumption was that the drop target was not being recognized. This is a totally different problem than what I had been trying to help you troubleshoot.
"I cannot drag and drop within Windows Explorer (sort of)
- I can drag and drop within the same Folder/subfolder structure, e.g. on the right side of Windows Explorer I can dnd a file to a subfolder but I cannot dnd a file over to the left side (This PC) to any of the folders, nas drives, san drives or local drives (shows red crossed through circle)"
Last part in brackets. Might not have found the right words to describe it though....
So, at the end of the rope and my patience.
Installed and tested 2 alternative Windows Explorer apps and they both let me drag and drop wherever I want.
So, this must be something within Windows Explorer blocking me, right? Or is that too simplistic?
Upgrading to 10147 solved the dnd issue. But even though I chose to upgrade and retain my old settings, some stuff windows just reset. One of those is the Libraries, Pictures, Downloads etc. folders in Explorer (which I removed through the registry). I have a slight suspicion that was the culprit. I'll fiddle with it a little later and see if it kills dnd again.