After creating a movie in iMovie 11, I attempted to burn it to a DVD. I
inserted a blank DVD and I got an error message that the disc slot was busy.

So I shut down the computer, ejected the blank DVD I had put in and then attempted to burn a DVD, but put the blank DVD in after I clicked on the circle which usually leads to burning the DVD. I got the same error message: that the disc area is busy. How do I remedy this? Thanks for any help.