title: Android Studio Gradle Error - preDexDebug
body: <p>I recently added a new activity to my android studio project and now I am getting an error when I try and run it. It builds fine but I get the error below when I run it:</p>
  
  <pre><code>FAILURE: Build failed with an exception.
  
  * What went wrong:
  Execution failed for task ':app:preDexDebug'.
  &gt; 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
  </code></pre>
  
  <p>Here is my build.gradle file</p>
  
  <pre><code>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')
  }
  </code></pre>
  
  <p>I have tried removing the supportLappcompat dependency but then I get even more errors. Any help greatly appreciated.</p>