Error In Android - Eclipse

Recently i started developing android applications, when compiling the application in the emulator the process is terminated. Follows the Logcat.

05-10 17:55:21.539: D/AndroidRuntime(4293): Shutting down VM
05-10 17:55:21.539: W/dalvikvm(4293): threadid=1: thread exiting with uncaught exception (group=0x40020578)
05-10 17:55:21.562: E/AndroidRuntime(4293): FATAL EXCEPTION: main
05-10 17:55:21.562: E/AndroidRuntime(4293): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{br.me.example.clientes/br.me.example.clientes.Principal}: java.lang.ClassNotFoundException: br.me.example.clientes.Principal in loader dalvik.system.PathClassLoader[/data/app/br.me.example.clientes-2.apk]
05-10 17:55:21.562: E/AndroidRuntime(4293):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1573)
05-10 17:55:21.562: E/AndroidRuntime(4293):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
05-10 17:55:21.562: E/AndroidRuntime(4293):     at android.app.ActivityThread.access$1500(ActivityThread.java:117)
05-10 17:55:21.562: E/AndroidRuntime(4293):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
05-10 17:55:21.562: E/AndroidRuntime(4293):     at android.os.Handler.dispatchMessage(Handler.java:99)
05-10 17:55:21.562: E/AndroidRuntime(4293):     at android.os.Looper.loop(Looper.java:130)
05-10 17:55:21.562: E/AndroidRuntime(4293):     at android.app.ActivityThread.main(ActivityThread.java:3687)
05-10 17:55:21.562: E/AndroidRuntime(4293):     at java.lang.reflect.Method.invokeNative(Native Method)
05-10 17:55:21.562: E/AndroidRuntime(4293):     at java.lang.reflect.Method.invoke(Method.java:507)
05-10 17:55:21.562: E/AndroidRuntime(4293):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
05-10 17:55:21.562: E/AndroidRuntime(4293):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)
05-10 17:55:21.562: E/AndroidRuntime(4293):     at dalvik.system.NativeStart.main(Native Method)
05-10 17:55:21.562: E/AndroidRuntime(4293): Caused by: java.lang.ClassNotFoundException: br.me.example.clientes.Principal in loader dalvik.system.PathClassLoader[/data/app/br.me.example.clientes-2.apk]
05-10 17:55:21.562: E/AndroidRuntime(4293):     at dalvik.system.PathClassLoader.findClass(PathClassLoader.java:240)
05-10 17:55:21.562: E/AndroidRuntime(4293):     at java.lang.ClassLoader.loadClass(ClassLoader.java:551)
05-10 17:55:21.562: E/AndroidRuntime(4293):     at java.lang.ClassLoader.loadClass(ClassLoader.java:511)
05-10 17:55:21.562: E/AndroidRuntime(4293):     at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
05-10 17:55:21.562: E/AndroidRuntime(4293):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1565)
05-10 17:55:21.562: E/AndroidRuntime(4293):     ... 11 more

Someone help me?