Can't get stage.focus to work on external loaded swf/images

Hi,

I’m pretty lost trying to make working the stage.focus on externally loaded swf or images.

The project : I got a main swf loading external images, animations, and videos.
For some of these files I need to keep control on buttons inside of these local stage.

So I thought I had to use the stage.focus = myMc.content to allow this but I’m getting a conversion error…

Please is there a solution?

Thank you!