ActionScript 3.0 :: Getting Error 1009 In Different Frame

I am scripting in an Actionscript 3.0 file, not in the timeline itself. I'm creating a point and click adventure where player move through different scene by clicking on the environment like normal point and click adventure game. I currently have only 2 frames. I put different scenes on different frame where player click the environment to move to that frame. However, when I put interactable movieclips and buttons in addEventListener on frame 2, I get:
TypeError: Error #1009: Cannot access a property or method of a null object reference.
at Puzzle1copy()

I ran debug and got this:
Attempting to launch and connect to Player using URL D:UserskikilalazDesktopNew SemGameProjectStuffPuzzle1CopyPuzzle1copy.swf
[SWF] D:UserskikilalazDesktopNew SemGameProjectStuffPuzzle1CopyPuzzle1copy.swf - 1183598 bytes after decompression
TypeError: Error #1009: Cannot access a property or method of a null object reference.
at Puzzle1copy()[D:UserskikilalazDesktopNew SemGameProjectStuffPuzzle1CopyPuzzle1copy.as:18]

Code:
Header 1package {
import flash.display.*;
import flash.events.*;
public class Puzzle1copy extends MovieClip {
public function Puzzle1copy() {
[Code] .....