I've run into a problem with 2.1 and toolbox. If I have a part that is already open that is in my toolbox parts and I try to drag another one in, I get a DRAG AND DROP FAILED. This happens if the part that is open is NOT in the directory that the toolbox part is located in. If I close the part out, it will drag & drop with no problem.
This used to give us a dialog box that the part was already opened, do you want to use this instead but still let us drop in the part.