[AS3] Help on Avoider Game Output Error

Hi guys,

I'm new to ActionScript3 and I'm getting some output errors on my Avoider Flash Game. I have my different stages in different frames but when the game advances to the next stage it starts to lag (I think its because its still running the actions from the first stage). After awhile it lags really badly.

Sorry if its a little confusing...I'm having a hard time adjusting to AS3.

I've attached a zip of my file and also, this is the error that Im getting...
code:
TypeError: Error #1009: Cannot access a property or method of a null object reference.

    at MB_Engine_Nav_v11_cs55_fla::MainTimeline/MoveMyTarget1()

TypeError: Error #1009: Cannot access a property or method of a null object reference.

    at MB_Engine_Nav_v11_cs55_fla::MainTimeline/MoveMyTarget2()

TypeError: Error #1009: Cannot access a property or method of a null object reference.

    at MB_Engine_Nav_v11_cs55_fla::MainTimeline/MoveMyTarget3()

TypeError: Error #1009: Cannot access a property or method of a null object reference.

    at MB_Engine_Nav_v11_cs55_fla::MainTimeline/MoveMyTarget4()

TypeError: Error #2007: Parameter hitTestObject must be non-null.

    at flash.display::DisplayObject/_hitTest()

    at flash.display::DisplayObject/hitTestObject()

    at MB_Engine_Nav_v11_cs55_fla::MainTimeline/begin()
I'd appreciate ANY help and THANKS in advance!