I'd like to implement Drag & Drop of files from Explorer to a Multiline TextBox on my form. The DragDrop Event should then fire to grab the FilePath of the file dropped and open it. But I'm falling at the first hurdle. I'm getting an error of 'The given key was not present in the dictionary'. This is caused by the DragDrop key. Other TextBox event types work fine in there, such as Click. Many Thanks.