I have similar issues but I think it may be related to whether the program is being "Run as Administrator" or not. I have a development tool that is set to always be run as administrator. I can't drap and drop to it from Windows Explorer even if I tell
it to run as administrator. The option to permanently set Windows Explorer to be run as administrator is grayed out.
I have another text editor, Notepad++. If I open that tool and then press ctrl-O to open a file in it, but instead of just opening a file, I drag the file to my development tool, I can't do it. The icon is the circle-slash icon. If I do the exact same
thing with Notepad++, but run it as administrator then I CAN drag and drop the file into my development tool. Not that this would be the approach to use, but it helps to further identify the real breakdown. Apparently you can only drag and drop a file into
a program which is running as administrator, from another program that is also running as administrator. Kinda makes sense, but its still a pain, especially since I can't get it to work from explorer.