Pizza Hut

Guys, i am doing a project here and turns out it always come out
TypeError: Error #1009: Cannot access a property or method of a null object reference.
at pizzaBaking/doRESTART()

i am so frustrated on how to debug it. This is the external actionscript(attached).

notes: when i typed gotoAndPlay(131), i still saw the MENUS,ABOUT,VOUCHER,UPDATES movieclips is still visible, but in fact i did type visible = false in the script. I want it to remain invisible until some button on stage triggered to become visible.
thank you very much.