FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':app:preDexDebug'.
> com.android.ide.common.internal.LoggedErrorException: Failed to run command:
    /Applications/Android Studio.app/sdk/build-tools/android-4.4W/dx --dex --output /Users/davidcavanagh/joshcpdandroid/app/build/intermediates/pre-dexed/debug/classes-22ecb8c50fefe43948d87c9fee8e36a6b7d1bb5a.jar /Users/davidcavanagh/joshcpdandroid/app/build/intermediates/exploded-aar/com.android.support/support-v4/20.0.0/classes.jar
  Error Code:
    1

apply plugin: 'com.android.application'

android {
    compileSdkVersion 20
    buildToolsVersion '20.0.0'

    defaultConfig {
        applicationId "com.joshcpd.android"
        minSdkVersion 15
        targetSdkVersion 20
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            runProguard false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile 'com.google.android.gms:play-services:5.2.08'
    compile 'com.android.support:appcompat-v7:20.0.0'
    compile project(':libraries:zbar')
}

buildToolsVersion 'android-4.4W'

buildToolsVersion '20.0.0'