[Solved] java.lang.IllegalStateException: You need to use a Theme.AppCompat theme (or descendant) with this activity

Recently Android SDK released a new update, and when you create a new application it automaticaly imports a library named Appcompat, when you try to compile and run the App you get this error in LogCat

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.txt2lrn.www/com.txt2lrn.www.LandingActivity}:
 java.lang.IllegalStateException: You need to use a Theme.AppCompat theme (or descendant) with this activity.
 at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651)
 at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
 at android.app.ActivityThread.access$1500(ActivityThread.java:117)
 at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
 at android.os.Handler.dispatchMessage(Handler.java:99)
 at android.os.Looper.loop(Looper.java:130)
 at android.app.ActivityThread.main(ActivityThread.java:3687)
 at java.lang.reflect.Method.invokeNative(Native Method)
 at java.lang.reflect.Method.invoke(Method.java:507)
 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)
 at dalvik.system.NativeStart.main(Native Method)
 Caused by: java.lang.IllegalStateException: You need to use a Theme.AppCompat theme (or descendant) with this activity.
 at android.support.v7.app.ActionBarActivityDelegate.onCreate(ActionBarActivityDelegate.java:102)
 at android.support.v7.app.ActionBarActivity.onCreate(ActionBarActivity.java:98)
 at com.txt2lrn.www.LandingActivity.onCreate(LandingActivity.java:95)
 at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
 at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615)
 ... 11 more

To solve this problem take a look in all your Activity files and check what your activity Extends, if it extends "ActionBarActivity" it's bad, because you should extend "Activity", make changes, import, save, Clear project and you are Done.