Variable to loaded swf issue

Hello

on frame 10 of my main movie I intent to load a swf which has a flv playing on the timeline + some animation.
the loaded movie is called “external_swf.swf”

in my complete handle this occurs:

var swf = MovieClip(loadEvent.currentTarget.content)
swf.my_text.text = “some text”;
addChild(loadEvent.target.content);

this works perfectly, aka on my loaded swf the textfield states my “some text”
and the flv (embedded on timeline) plays + all animation works as planned.

However, the moment I want to trace something out on the loaded timeline i get this error
TypeError: Error #1009: Cannot access a property or method of a null object reference.
at main_fla::MainTimeline/frame1()

the flv on the timeline does not play.

my trace is simply:
trace("what is in the textfield: " + my_text.text);
my_text is def. on the loaded movie’s timeline.
Even with not tracing something out , but fe. declaring a var as:
var newVar:String = “hello iam the loaded movie”

freezes the process and i get the type error.

Any ideas? This is highly weird to me.