Buttons within a movie clips

1

I have 5 movie clips (that behave like buttons) in a movieclip. They animate in. The parent is called menuAnim and is on the main timeline.

When the button animation stops (frame 35) I want to add event listeners to the buttons. I have treid this

stop();
aboutus_but.addEventListener(MouseEvent.CLICK, MovePage);

I get

1120: Access of undefined property aboutus_but.

I have given the buttom the instancename (about_but);