ActionScript 3.0 :: Implementing Pause Function In Game?

I'm implementing a pause function in a game, it stops the main game timer and then dispatches an event ("Game_Paused") to stop a second timer. Both timers stop (and start) correctly but the second one throws a null object reference error.

Here's the ActionScript Code:
private function onAddedToStage(e:Event):void{
_timerD = new Timer(100);
_timerD.start();
_timerD.addEventListener(TimerEvent.TIMER, onUpdateTime);
stage.addEventListener("Game_Paused", onPauseGame);
[Code] .....

And this is the output:
Code:
Paused Timer=null
TypeError: Error #1009: Cannot access a property or method of a null object reference.
at com.rtr.game.UI::timer_display/onPauseGame()
at flash.events::EventDispatcher/dispatchEventFunction()
at flash.events::EventDispatcher/dispatchEvent()
at flash.display::Stage/dispatchEvent()
at com.rtr.game::Game_Timer/onKeyDown()
Paused Timer=[object Timer]

What's really confusing me is that the timer is still getting paused correctly, and the trace is showing up in the output before and after the error with two different objects.