Had the same issue again this morning. I was unable to apply the fix stated above, when trying to add the downloaded file back to the correct folder, it gave me an error message saying I lacked permission to move files to that folder (strange as I am an admin on my computer. You were correct about the antivirus removing the file however, I use Avast and when I checked the virus chest I found the missing file and was able to restore it to the folder from there.