Android - 无法执行dex：多个dex文件定义

我试过运行我的Android应用程序，我得到这个错误。

I tried run my android app and i got this error.

[2014-03-11 11:21:34 - Dex Loader] Unable to execute dex: Multiple dex files define Lorg/apache/cordova/App$1;
[2014-03-11 11:21:34 - Android-C2DM-PhoneGap] Conversion to Dalvik format failed: Unable to execute dex: Multiple dex files define Lorg/apache/cordova/App$1;

我使用这个项目来参考。
http://devgirl.org/2012/10/25 / tutorial-android-push-notifications-with-phonegap /

I'm using this project for my reference. http://devgirl.org/2012/10/25/tutorial-android-push-notifications-with-phonegap/

我为我的项目使用电话差距。

I'm using phone gap for my project. I export external cordova lib project into my android project.

为什么会发生？