I think you're trying to compile AS3 code with AS2 compiler. Try changing your compilation settings to target AS3. Also you may need to include the class import at the top of your code:
import flash.events.MouseEvent;
To drag 50 objects, add them all on the same container sprite and add the listener to the container sprite only:
var holder:Sprite = new Sprite();
for ( var i:int = 0, l:int = 50; i < l; i++ ) {
var dragee:YOUR_CUSTOM_OBJECT = new YOUR_CUSTOM_OBJECT();
holder.addChild(dragee);
}
addChild(holder);
holder.addEventListener(MouseEvent.MOUSE_DOWN, mouseDownHandler);
holder.addEventListener(MouseEvent.MOUSE_UP, mouseUpHandler);
holder.addEventListener(Event.MOUSE_LEAVE, mouseUpHandler);
var currentDragee:YOUR_CUSTOM_OBJECT = null;
function mouseDownHandler(evt:MouseEvent):void {
currentDragee = evt.target as YOUR_CUSTOM_OBJECT;
if ( currentDragee !== null ) {
currentDragee.startDrag();
holder.addChild(currentDragee); // bring current to front position
}
}
function mouseUpHandler(evt:Event):void {
if ( currentDragee !== null ) currentDragee.stopDrag();
currentDragee = null;
}
YOUR_CUSTOM_OBJECT being the object class you need to drag. Hope it helps!