Exception loading Facebook Login Button in Android Studio

I want to make an app with facebook integration. I'm using Android Studio 1.1.0. I'm able to import the facebook skd 4.0.0 in build.gradle (Module:app) and use it in the Java code:

apply plugin: 'com.android.application'

android {
    compileSdkVersion 21
    buildToolsVersion "22.0.1"

    defaultConfig {
        applicationId "package.test"
        minSdkVersion 15
        targetSdkVersion 21
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

repositories {
    mavenCentral()
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile 'com.android.support:appcompat-v7:22.0.0'
    compile 'com.facebook.android:facebook-android-sdk:4.0.0'
}

I also put the LoginButton into the layout file from my activity:

<RelativeLayout xmlns:android="http://ift.tt/nIICcg"
    xmlns:tools="http://ift.tt/LrGmb4"
    ...
    tools:context=".MainActivity">

    <com.facebook.login.widget.LoginButton
        android:id="@+id/login_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_marginBottom="30dp"
        android:layout_marginTop="30dp" />

</RelativeLayout>

This exception is thrown at setContentView(layoutfile).

I already checked the samples in facebook sdk on github but it doesn't helped me to fix this problem. Is the import of facebook sdk correctly?

Thanks in advance!