title: Error: buildToolsVersion is not specified
body: <p>This is a follow up question to this question:</p>
  
  <p><a href="https://stackoverflow.com/questions/32153544/errorcause-buildtoolsversion-is-not-specified">Error:Cause: buildToolsVersion is not specified</a></p>
  
  <p>I just imported a project from Eclipse to AS. It had another project which was a library project and the main project used it as a library. At first, AS imported that library project as a Java project and put "apply plugin 'java'" which I believe was a cause of other issues which made the compiler not recognize symbols like com.android.Toast. I changed the plugin to <code>apply plugin: 'com.android.library'</code> and now I get </p>
  
  <blockquote>
    <p>buildToolsVersion is not specified</p>
  </blockquote>
  
  <p>My outer project's gradle.build:</p>
  
  <pre><code>// Top-level build file where you can add configuration options common to all sub-projects/modules.
  buildscript {
      repositories {
          jcenter()
      }
      dependencies {
          classpath 'com.android.tools.build:gradle:2.2.2'
      }
  }
  
  allprojects {
      repositories {
          jcenter()
      }
  }
  </code></pre>
  
  <p>And the module's build.gradle:</p>
  
  <pre><code>apply plugin: 'com.android.library'
  
  dependencies {
      compile 'com.google.code.gson:gson:2.6.2'
      compile files('libs/commons-lang3-3.4.jar')
      compile files('libs/linphone.jar')
      compile '__local_jars__:C:\\Users\\me\\Android Studio Projects\\MyProj\\tigris\\libs\\firebase-client-android-2.5.0.jar:unspecified'
      compile '__local_jars__:C:\\Users\\me\\Android Studio Projects\\MyProj\\tigris\\libs\\firebase-client-android-2.5.0.jar:unspecified'
  }
  </code></pre>
  
  <p>Why is it happening? </p>