This Treads are no solution.
I had the same problem.
Cause:
The new jquery library 3.1.x doesn't support any more
jQuery.event.props.push("dataTransfer");
so the developer removed this line in ./js/filedrop.field.js on Line 295
But they forgot to change a variable, which appends on it.
So change the variable on function drop(e), to find on line 362
function drop(e) {
if( opts.drop.call(this, e) === false ) return false;
if(!e.dataTransfer)
return;
files = e.dataTransfer.files;
to
function drop(e) {
if( opts.drop.call(this, e) === false ) return false;
if(!e.originalEvent.dataTransfer)
return;
files = e.originalEvent.dataTransfer.files;
Now, drag and drop schould work again...
