Getting an error trying to make WASD movement work

Hi everyone

I am trying to make a character move using the W, A, S, D kets but I am getting a big error. Every time I test the code it says:

Coercion failed: cannot convert flash.events to flash.events.KeyBoardEvent

Here is my code thus far:

stage.addEventListener(KeyboardEvent.KEY_DOWN, gameLoop);
function gameLoop (event:KeyboardEvent):void{

if(event.keyCode == 65)
{
    xspeed = xspeed-power;
}

There is more, but this is the stuff just having to do with movement using the keys. What am I doing wrong??