Firstly, i don't think you mean "unload", do you? Oh well, just gonna assume you mean "load"..
You do get the trace "file loaded", don't you?
But you're not seeing the content on screen? Is that your problem?
Use:
ActionScript Code:
var swfLoader1:Loader = new Loader();
var bgURL1:URLRequest = new URLRequest("mainevent.swf");
swfLoader1.contentLoaderInfo.addEventListener(Event.COMPLETE, loadProdComplete1);
swfLoader1.load(bgURL1);
function loadProdComplete1(e:Event):void {
trace("file loaded");
mainevent.addChild(e.currentTarget.content);
}