copying to external drive yields strange error

I am copying "stuff" to my new 4TB external HDD = F:\ >> from an internal drive Z:\
Things seem to go OK for a while, then I get this error message

==========
Could not find this item
This is no longer located in F:\Video. Verify the item's location and try again.
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If I attempt to D&D anything else I get the same error.
Another one of Windoz' 7 jokes I assume.

I am copying via D&D and total files is about 200GB - only 11.6GB copied.
The first time I did it there was no issue. The 2nd and 3rd time I had to unplug to get it to reset.

It is correct that the folder no longer exists at that location because it never has been there.
That is where it is copying TO.

So what is up?
thx

If the message occurs when using other methods, such as copy & paste, instead of drag & drop, then I would check to see if the OS recognizes the external F: in its full capacity. Next on the list would be hardware limitations.

D&D = drag & drop

apparently it is windows explorer that is getting confused.
Of course the file or folder doesn't exist on F:. It hasn't been copied there yet.
AND it is not suppose to copy it FROM the F: drive.
When I first plug it in everything is good. The copy starts and copies a lot - then WE barfs all over.
Something happens to WE during the process.
Unplugging and replugging F: and restarting WE clears it till the next time.
I can't even do a copy from C: to C: - same message unless I unplug F: and restart WE.