My code Event.ENTER_FRAME could not be loaded.

Hi I'm rather new with AS3 and I made a new code for a game where a character picks up coins that looks like:

stage.addEventListener(Event.ENTER_FRAME, gameloop);

function gameloop(evt:Event) {

    pickUp();

}

function pickUp(){

    if (car1.hitTestObject(coin1)){

        coin1.x=1500;

    }

    if (car1.hitTestObject(coin2)){

        coin2.x=1500;

    }

    if (car1.hitTestObject(coin3)){

        coin3.x=1500;

    }

}

However, it says the class or interface "Event" could not be loaded.

Please help me.

Thank you.