为什么用debug模式运行下面这么简单的代码，会出这种异常

为什么用debug模式运行下面这么简单的代码，会出这种错误？
package {
import flash.display.Sprite;

public class AS_0100_HelloWorld extends Sprite
{
public function AS_0100_HelloWorld()
{
trace("HelloWorld");
}
}
}


Flex Builder给出的错误信息是：
Failed to connect; session timed out
Ensure that:
 1.You compiled you Flash application with debugging on.
 2.You are running the debugger version of Flash Player.

------解决方案--------------------
http://www.adobe.com/support/flashplayer/downloads.html
debug版的下载