duplicate movieclip problem

it says is the manual that one can use this function to duplicate a movie clip:
duplicateMovieClip(target, newname,depth)

I want to duplicate an MC named goal. I put the following code an a button, but it doesn't work.

duplicateMovieClip(_root.goal, "unique_namexxx", 109)

this one doesn't work either:
duplicateMovieClip(goal, "unique_namexxx", 109)

I even right-clicked on the 'goal' MC on the library, went to linkage, clicked 'export for actionscript', gave it a name of 'goal_link' and then did this:
duplicateMovieClip(_root.goal_link, "unique_namexxx", 109)

and this:
duplicateMovieClip(goal_link, "unique_namexxx", 109)

and this:
duplicateMovieClip("goal_link", "unique_namexxx", 109)

and it didn't work. The only way I can get it to work is if I put an instance somewhere on the stage and then do this



but I don't want to do it this way. Why isn't it working?

duplicateMovieClip() method requires that you alread have a clip on the stage.

if you don't want to do that, use attachMovie() instead.