Problem with an addChild item!?!

hi all i am having a minor issue with a child that i am trying to add to a movieclip on the stage the movielip is the basic menu and colours and im trying to add the menu txt and set it to the right position however i keep getting an error and i cant spotwhy and its doing my head in the rror says:

TypeError: Error #1010: A term is undefined and has no properties.

i have found the 2 lines of code that are causing the issue and they are highlighted in red below and i hope someone can help me with this. thanks.

var navTxt:MovieClip = new MenuText();

menuHolder.x = 0;
menuHolder.y = 595;
menuHolder.width = stage.stageWidth;
menuHolder.height = stage.stageHeight / 2.5;
menuHolder.addChild(navTxt);
[COLOR="Red"]menuHolder.navTxt.x = menuHolder.width / 2;
menuHolder.navTxt.y = 30;[/COLOR]