This happens when you choose your hard drive as the target in the SAVE TO box. To correct the problem, all you need to do is select your burner in the SAVE TO box as the target, then it will ask for a blank disc for the copying process.
As for a movie source on your hard drive, you can load it as source to DVDFab Copy-Clone/Burn mode to burn it to blank media directly, so you don't need to go through the copy process again.