There is a good chance that the shift cable end bushing has worn out and allowed the cable to pop off the trans. As a temp repair you can tie it back up with a nylon tie.
For much more detail about this, see my post from about a year ago "it finally happened".
You can replace just the shift cable end, and even better, you can swap the bushing out of the new end so that you don't have to remove the old cable end and go through the hassle of adjusting.
Some dealers may tell you that you must replace the entire cable. You should call Bill Jenkins at Team Ford in Las Vegas. He should still be able to get the ends by themselves.
