java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.exa

最近做安卓项目，按照helloworld做了一个安卓例子，启动报错如下（折腾了很久，始终没有找到解决办法）：

java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.xibaoming4/com.example.xibaoming4.MainActivity}: java.lang.ClassNotFoundException: com.example.xibaoming4.MainActivity

测试模拟器参数：
Plateform:4.0
API Level:14
CPU/ABI:ARM(armeabi-v7a)

调试报错信息：
12-24 16:44:56.349: W/dalvikvm(735): threadid=1: thread exiting with uncaught exception (group=0x409961f8)
12-24 16:44:56.369: E/AndroidRuntime(735): FATAL EXCEPTION: main
12-24 16:44:56.369: E/AndroidRuntime(735): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.xibaoming4/com.example.xibaoming4.MainActivity}: java.lang.ClassNotFoundException: com.example.xibaoming4.MainActivity
12-24 16:44:56.369: E/AndroidRuntime(735): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1879)
12-24 16:44:56.369: E/AndroidRuntime(735): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1980)
12-24 16:44:56.369: E/AndroidRuntime(735): at android.app.ActivityThread.access$600(ActivityThread.java:122)
12-24 16:44:56.369: E/AndroidRuntime(735): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1146)
12-24 16:44:56.369: E/AndroidRuntime(735): at android.os.Handler.dispatchMessage(Handler.java:99)
12-24 16:44:56.369: E/AndroidRuntime(735): at android.os.Looper.loop(Looper.java:137)
12-24 16:44:56.369: E/AndroidRuntime(735): at android.app.ActivityThread.main(ActivityThread.java:4340)
12-24 16:44:56.369: E/AndroidRuntime(735): at java.lang.reflect.Method.invokeNative(Native Method)
12-24 16:44:56.369: E/AndroidRuntime(735): at java.lang.reflect.Method.invoke(Method.java:511)
12-24 16:44:56.369: E/AndroidRuntime(735): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
12-24 16:44:56.369: E/AndroidRuntime(735): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
12-24 16:44:56.369: E/AndroidRuntime(735): at dalvik.system.NativeStart.main(Native Method)
12-24 16:44:56.369: E/AndroidRuntime(735): Caused by: java.lang.ClassNotFoundException: com.example.xibaoming4.MainActivity
12-24 16:44:56.369: E/AndroidRuntime(735): at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:61)
12-24 16:44:56.369: E/AndroidRuntime(735): at java.lang.ClassLoader.loadClass(ClassLoader.java:501)
12-24 16:44:56.369: E/AndroidRuntime(735): at java.lang.ClassLoader.loadClass(ClassLoader.java:461)
12-24 16:44:56.369: E/AndroidRuntime(735): at android.app.Instrumentation.newActivity(Instrumentation.java:1023)
12-24 16:44:56.369: E/AndroidRuntime(735): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1870)
12-24 16:44:56.369: E/AndroidRuntime(735): ... 11 more

系统环境：
Android DDMS 23.0.4.1468518
Android Development Tools 23.0.4.1468518
Android Hierarchy Viewer 23.0.4.1468518
Android Native Development Tools 23.0.4.1468518
Android Traceview 23.0.4.1468518
Eclipse IDE for Android Developers 23.0.2.1259578
Tracer for OpenGL ES 23.0.4.1468518


各种办法都尝试了
1、项目属性，order and export下的android private libaraies勾选过了。
2、manifest.xml文件也检查过了。
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.xibaoming4"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="14"
android:targetSdkVersion="21" />
<uses-permission android:name="android.permission.INTERNET"/>
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@android:style/Theme.Dialog">
<activity android:name=".MainActivity" android:label="xibaoming4">
<intent-filter android:label="@string/hello">
<action android:name="android.intent.action.MAIN"></action>
<category android:name="android.intent.category.LAUNCHER"></category>
</intent-filter>
</activity>
</application>
</manifest>

3、项目也clean过了...

还有什么办法？请各位高手指教！