Problem calling variable on main timeline from external SWF

Hey guys, I’m cracking my head with this one. As the title reads I’m in the middle of a nightmare trying to retrieve a variable on the main timeline from a SWF loaded with the loader class.
Thing is I used this line within the loaded SWF:

var actua:String= MovieClip(stage.getChildAt(0)).seccion;

It does rerieve the value still it drops the next error:

TypeError: Error #1009: Cannot access a property or method of a null object reference.
at protection_fla::MainTimeline/datos()[protection_fla.MainTimeline::frame1:10]

“protection_fla” is the loaded SWF and the line the error points to (frame1:10) is where “var actua:String…” is located. How come it takes the value for NULL since it does grab it? Is there another way to call variables from the main timeline which isn’t this buggy?Any advice much appreciated. Thanks.