Please help with converting comboBox from AS2 to AS3

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I’m in the beginning stages of trying to understand AS3.
Flash is outputting these two errors:

1118: Implicit coercion of a value with static type Object to a possibly unrelated type Function.

1120: Access of undefined property event_obj.

my_cb.addItem({data:1, label:"First Item"});
my_cb.addItem({data:2, label:"Second Item"});
my_cb.addItem({data:3, label:"Third Item"});

// Create Listener Object.
var cbListener:Object = new Object();

// Assign function to Listener Object.
cbListener.change = function(evt_obj:Object) {
trace("Value changed to: "+event_obj.target.selectedItem.label);
};

// Add Listener Event.
my_cb.addEventListener("change", cbListener);

cbListener.change = function(evt_obj:Object) {
	var itemName:Number = new Number();
	itemName = evt_obj.target.selectedItem.data;
	if(itemName == 1) {
		gotoAndPlay(1);
	}
	else if(itemName == 2) {
		gotoAndPlay(20);
	}
	else if(itemName == 3) {
		gotoAndPlay(30);
	};
}

Please help