title: Build fails in Android Studio after adding library
body: <p>I've been using Android Studio 1.0.2 for a while now and have had no problems. I have a fairly simple app that uses Fragments. Originally I was using the built-in Fragment framework as my target devices will be 4.0.2 upwards. However, due to bugs in the Framework on earlier devices I decided to move to using the Fragment support library (why anyone would not use this over the built-in - well, that's another question...)</p>
  
  <p>I added the library, com.android.support:support-v4:21.0.0, to my build.gradle, thus:</p>
  
  <pre><code>dependencies {
      compile 'com.android.support:support-v4:21.0.0'
      compile 'com.google.android.gms:play-services:+'
      compile 'com.google.code.gson:gson:2.2.4'
      compile 'com.amazonaws:aws-android-sdk-core:2.1.5'
      compile 'com.amazonaws:aws-android-sdk-s3:2.1.5'
      compile 'com.android.support:appcompat-v7:21.0.3'
  }
  </code></pre>
  
  <p>(I already had appcompat-v7 in the list).</p>
  
  <p>All good so far. After converting the fragment manager calls and imports I did a build and got this:</p>
  
  <blockquote>
    <p>Error:Execution failed for task
    ':app:prepareComAndroidSupportAppcompatV72103Library'. Failed to
    create parent directory
    'D:\current-projects\android_studio_projects\WallPaintings\app\build'
    when creating directory
    'D:\current-projects\android_studio_projects\WallPaintings\app\build\intermediates\exploded-aar\com.android.support\appcompat-v7\21.0.3'</p>
  </blockquote>
  
  <p>I performed a synchronise and then I did an Invalidate Cache and restart. I then performed another build and got the same result.</p>
  
  <p>Then, after some reading on SO, I discovered you have to perform a "Synch Project with Gradle files". I did this and it worked - compiles up, builds the APK, etc. Fantastic.</p>
  
  <p>However, from that point on, every time I do a Clean or a Rebuild I end up with the same error until I perform the gradle synch.</p>
  
  <p>What is the problem? I can't see what I've done wrong. There is ample disk space and the directory where it attempts to create the things is read/write.</p>
  
  <p>Or is this yet another piece of black-box magic / dark arts that one needs to learn in order to use Android Studio (come back Eclipse - all is forgiven!!)</p>